"You don't like the way I phrased an answer. What kind of evidence is that?"
—The guy who did it, Monk, "Mr. Monk Fights City Hall"
The classic whodunit challenges the viewer to solve the crime along with the detective. Since the viewer isn't a professional, the crime has to be set up so that the solution doesn't rely on skills only a professional criminologist would have. These mysteries often work by reducing the crime to a logic puzzle: you solve the mystery by finding the fact that doesn't fit.
The problem with this is the "solution" at the back of the book doesn't give the perp a chance to offer a perfectly reasonable explanation.
Real crimes aren't logic puzzles and mere factual inconsistencies aren't a substitute for hard evidence. Poking holes in a suspect's story might push a jury towards the edge, but it's not going to convince them by itself. You might be able to Pull the Thread, but on its own, proving that the suspect lied about something doesn't prove he committed the crime (especially if he has a Big Secret). At best, this kind of logic game can be used during Perp Sweating to get a confession. At worst, Detective Brown will arrest the perp immediately, but Perry Mason wouldn't even break a sweat getting an acquittal from that.
The level to which this trope is justified depends on what the contradiction is being used to prove. A novel explanation for a baffling set of circumstances can give the police a new avenue for their investigation. Inconsistencies in a person's story may not be enough to prove they committed a crime but it can prove they lied to the police and that would be enough to pursue warrants or get them on a charge such as obstruction of justice that could lead to other more tangible forms of evidence. However, in countries where the accused is innocent until proven guilty, a "logical flaw" in the perp's alibi will make for a strong circumstantial case at best, but it far from meets the standard of proof of "guilty beyond a reasonable doubt".
For this reason, most examples realistically focus on the investigative side, where the contradiction satisfies the significantly lower standard of proof required to arrest someone, without dwelling on the Fridge Horror of whether the merits of the case meet the "Prima facie" burden required to convict them. However, some stories allow the handwave that the contradiction inevitably leads to the find of real evidence; or else unnerves the villain into Villain Decay and Motive Rant. As such, Justifying Edits are not necessary, and points that have these still fit if the actual "conviction" is simply tacked on to the end of the story.
On the other hand, a logical inconsistency in the testimony of a key witness for the prosecution can blow a hole in the case. If the witness claims to have seen something they could not possibly have seen, or could not possibly have seen the way they claim to have seen it, it puts the testimony in doubt. Which creates exactly the kind of "reasonable doubt" that allows the accused to walk. In short, casting doubt on the prosecution's case doesn't require proving someone else did it or that you're innocent; only that the case against you is questionable enough to think you might not have done it.
In most stories involving teenage perpetrators, the crimes are rather minor and the solution has them immediately confess as a result of being "trapped by his/her lie." It's more egregious when it's shown to work against adult suspects who are assumed to know their rights and to remain silent or ask for a lawyer when the police suspect them of a crime. But then again, Only Bad Guys Call Their Lawyers.
See also Conviction by Counterfactual Clue, which is when the "flaw" found to prove the suspect's guilt is simply erroneous. This overlaps with Hyper Awareness — sometimes it's just hyper-awareness taken too far, to the point of noticing details that logically shouldn't even be noteworthy. Can lead to a minor Inferred Holocaust, if logic dictates that the supposedly happy ending will lead to either a guilty character escaping or an innocent one being convicted. These types of inferences often run afoul of Hanlon's Razor, blaming every flaw or contradiction on lies and conspiracy rather than, say, faulty memory or panic.
Compare I Never Said It Was Poison, where the suspect demonstrates knowledge of a detail or two they shouldn't.
This gets particularly egregious when the story contains perfectly good alternative clues, but the flimsy one was chosen as The Clue.
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This has happened so often in Encyclopedia Brown shorts that the former Trope Name was Bugs Meany Is Gonna Walk.
A "witness" trying to frame a boy for the theft of a pocket knife claims the boy took the knife with his right hand, and put it in his pocket while running away. He is found innocent because he has a cast on his left hand and the knife was found in his left pants pocket (planted there by the "witness") and (according to the answers section at least) it's impossible to put a pocket knife in your left pants pocket with your right hand while running. Leaving aside that Encyclopedia was assuming an impossibility out of a difficult, and highly improbable physical stunt, the mere likelihood of him putting the knife in his left pocket after he'd stopped running never occurred to him. Of course, since the inconsistency here is being used on the defendant's behalf to create reasonable doubt, it's more valid than most of the other examples on this page.
The perp claims to have been out of town during the crime, but knows details about some contemporaneous local event (because, clearly, he never talks to anyone about local events or reads newspapers).
The perp claims to have seen something by moonlight on a night when there was no moon. It's entirely possible that the perp saw the incident by another ambient source of light and simply assumed it was moonlight. Interestingly, Abraham Lincoln got an acquittal in a case in exactly this manner, though in his case it was used to show that, without moonlight, it would have been impossible to see something 150 ft away at night in 1858.
A boy blows his fake alibi by tracing a shirt pocket on the wrong side of his chest. This is perfectly understandable, since everyone is accustomed to seeing images of themselves in the mirror, where left and right are flipped.
A man accused of committing a robbery is being interrogated in the crime scene and claims he has never been there before. Shortly afterward, he says, "When you brought me back here, did I resist?" to the police officer. Since he couldn't be brought back if he had never been there before, the man is guilty. First of all, the term "back" doesn't have to mean "return." It can simply indicate distance or location, shown in common phrases such as, "He's from back east." You can also say you're taking someone "back" somewhere if you've already been there. The all-too-common example would be asking a stranger, "Want to go back to my place?"
A perp claims to have been on the bottom floor of a building when the crime was committed, yet when he went to the elevator, he pressed the "up button." Encyclopedia deduces that the perp was probably not on the very bottom floor, because the perp wouldn't have had to distinguish the button as the "up button" because there wouldn't have been a "down button." Of course, an "up button" is always an "up button" whether or not there's a "down button" along with it. The actual name for them is "call button", but it's rarely used outside of technical and legal documentation. Besides, plenty of call buttons still have the appropriate arrow on them even when they're on the top and bottom floors.
The perp tells someone he's hidden a $2 note between an odd and even page of a book that are normally on opposite sides of a leaf if the book is read left to right. It might be possible that the book had a typo, breaks the tradition, had its pages printed out of order, or the perp simply misremembered the book pages. Either way, this is one of the mysteries that has an obvious answer of simply looking at the book or checking out a copy of it to prove he's lying but Brown insists on over-thinking the solution.
The perp didn't name the book but instead just said it was in the 'gray book on the table', and there wasn't actually a book on the table (the victim assumed the librarian reshelved it in the interim), so looking at the book wasn't an option.
A stolen rare coin is found inside Bugs Meany's hot dog. How did Encyclopedia know where to find it? Because he saw Bugs spread mustard on top of the sauerkraut, and "no one wholikes hot dogsdoes that." Admittedly, it is a pretty messy way to go about things (similar to trying to spread peanut butter on top of jelly), but c'mon. Interestingly, the story effectively admits Bugs would have walked if he'd been willing to finish his hot dog, and presumably swallow the coin in the process. Also a case of Technology Marches On, as a modern reader would expect the mustard to come out of a squeeze bottle and be easier to have on top than the sauerkraut. Plus, who's to say Bugs hadn't just overlooked the mustard jar, or that someone else was hogging it, when he first started applying his hot dog toppings?
The perp buys time to rob his victim's house by asking the victim to add four tubes of toothpaste to his supermarket order of seven items. This required the victim to check out in a regular shopping lane instead of the 10-items-or-less express lane, which otherwise would have allowed him to return in time to see his house being robbed. Brown figures it out because the perp was the last of the victim's friends to ask for items, and his order was too plainly designed to surpass the Express Lane Limit. Of course, the fact that the perp counted on both the victim and grocery staff to obey the letter of the express lane rules and for the express lane line to be open and available at the same time he was at the store pretty much means he deserved to get caught.
Bugs Meany holds a raffle drawing at a fair for a baseball glove and has one of his friends reach around for another associate's balls in the big container of ping-pong balls. Encyclopedia discovers he was cheating by noticing that Bugs drank a canned soda when he was carrying around a thermos, thus meaning he put the ball in the freezer, then took it to the fairgrounds in the thermos so the associate would just have to feel around for a frozen ball. It's entirely possible that Bugs simply didn't want whatever was in his thermos at that particular moment or was saving it for later. Or that he'd already emptied his thermos, and found himself wanting another drink.
A carnival tent gets upended, and the take is stolen in the confusion. When Encyclopedia studies the injuries of the performers, he suspects the magician; the reason? He's wearing a short-sleeved outfit, and "all magicians wear long sleeves to hide things in." This example is also listed under Conviction by Counterfactual Clue.
Two precious ivory bookends belonging to a former circus owner are stolen when two of the man's friends are visiting. Encyclopedia and his father find strange handprints in the beach near the circus owner's house, and so suspicion falls on one of the visitors, a crippled acrobat, because the only way he could have walked was on his hands. Encyclopedia, however, insists that the thief is in fact the other visitor, a former bareback rider, because she said her leather gloves were missing, and "no one brings leather gloves to a seaside town in the summer." (Because she couldn't possibly have brought the gloves for a legitimate reason like playing golf, as driving gloves, or even riding a horse. And she certainly couldn't have packed them by accident.)
A perp who's trying to frame Encyclopedia for claiming ownership of the town clock and charging people to use it to set their watches is "proved" as a liar because he used his left hand to set his own watch, because of the "fact" that when you set your watch with your left hand, you're holding it upside down. (Because it's impossible that a person could simply be more comfortable using their left hand, and compensate for it when setting their watch, or that one could buy left-handed watches specifically to avoid this problem.)
A perp is accused of stealing something that belonged to Encyclopedia's client, and riding away on her bicycle. She claims that she hasn't ridden her bike all summer, before she takes it out of storage and starts showing off on it. Encyclopedia declares that she's lying, because if she hadn't ridden the bicycle like she claimed, the tires would have gone flat. (Because it's impossible that the girl or her parents could have kept the tires inflated in case she ever decided she wanted to go for a bike ride.)
A man tries to claim insurance money on a painting he's reported stolen. His story goes that while shaving after a shower, he saw reflected in the mirror a man stalking away with the painting. Encyclopedia explains that the claim is a fraud because a mirror would be foggy after a shower and so the man wouldn't have been able to see anything. (Never mind that it only takes a second to wipe away condensation, something people often do when they need to shave. Or cold showers, or how movement and shapes are still discernible through a foggy mirror. Or how some people use a fan or leave the bathroom door open specifically so that the mirror doesn't fog up in the first place!)
A sailor wins a painting contest open only to amateurs. He is called out as a professional painter pretending to be a sailor because he failed to do the research on nautical terminology: he used terms like "left" or "right" when describing a boat he was painting rather than the nautical terms like "port" or "starboard", as well as the redundant phrase "knots per hour,"note A knot is a unit of speed referring to approx. 1 nautical mile per hour. Technically, this would be acceleration, mistakes that no one remotely familiar with sailing would have made regardless of their expertise level. However, while "he's a professional painter trying to pass as an amateur" is the most likely explanation for the masquerade and was probably sufficient grounds on its face to get him disqualified, he might have had other reasons for the pretense and it's not ironclad evidence he's an actual professional.
Still another case hinged on the detective's belief that a real resident of San Francisco would never ever refer to the city as "Frisco." While it's true that residents of the city traditionally hate that nickname, it's not exactly an enforced law, at least not since Emperor Norton died.
A case had a kid that finished last in a race correctly identify a song being played at a theater along the race route as "The Eyes of Texas," rather than (the presumably more identifiable to a kid in Idaho) "I've Been Working on the Railroad," "proving" that he stopped in to ensure that he would finish last. Because he couldn't simply have been a football fan who had seen the Longhorns play. This compounded by the fact that the two songs aren't even the same - "I've Been Working on the Railroad" has more lines, to a different tune.
A blind man is the only witness to a crime; a perp fleeing the scene with a bag of cash crashed into him, and it is thought that the man might have felt his face well enough to identify him if he felt it again. Turns out the blind man is not blind, and was in on it the whole time: he swapped bags with the thief when they collided. How does Encyclopedia prove this? When he visited the man in his hotel room, the lights were on and there was a newspaper on the table despite the man claiming he hadn't had visitors in "a long time". Because no hotel in the world offers complementary newspapers that they put in your room. And they never have the lights on when you arrive. And a blind man would totally notice if they were on, and turn them off. This is a lesser example, however. Once Brown figures out what happened getting a doctor to confirm that the guy can see shouldn't be too hard.
Bugs steals an antique teacup. When Encyclopedia confronts him about it, Bugs claims that that it was a prized cup from the owner of a Chinese restaurant that has since gone out of business. Encyclopedia deduces that he's lying by noticing that the cup has a handle, which Chinese teacups do not have. (Because it's impossible for a Chinese guy to like American mugs.)
One story had a girl having one of her sneakers stolen from her before a sneaker contest was held. The thief was identified because she said to another person that the girl had the sneaker stolen from her "while clipping her toenails", even though all the girl said was that she was "clipping her nails". And only the thief would know that she had been clipping her toenails and not her fingernails (Even though if someone said she had her sneaker stolen while clipping her nails before a contest involving feet, most would immediately assume the nails WERE toenails, not fingernails.) There's no reason to take your shoes off to clip your fingernails, and it's a safe bet a person would notice someone stealing shoes that they were wearing at the time, making it even less of a stretch to assume that toenails were meant.
Another story involved Encyclopedia Brown solving a case because a suspect came to the door with tears dripping from the outside corners of her eyes; from this Encyclopedia deduced that she was faking tears, since tears come from the INSIDE corners of your cheek. Where tears really overflow from the eye's surface onto the cheeks depends on the structure of the individual's eyes, how puffy and irritated they are, and the tilt of the weeping person's head, among other things.
Encyclopedia's dad described a case to him after the fact that involved a professional tennis instructor who reported that a set of ivory screens had been stolen that morning. He saw the thief's face; it could be either of two identical twins — one who worked as a cashier and one who played tennis. Encyclopedia figured out that the victim was just lying so he could get insurance money for the screens. The incriminating evidence? The crook was wearing a T-shirt, and if the tennis player had been the culprit, one arm would be more developed, while equal arms would incriminate the cashier. Granted, the "victim" was also a tennis player and was familiar with the twins, but being tied to a chair with a gunman in your house is not the time to expect Holmes-level analysis. More likely, his head held no thoughts but "call 911".
Not to mention the fact that all a person has to do is look up a picture of a professional tennis player to realise this theory doesn't really work. Unless the tennis player is intentionally flexing their biceps to show off the muscles in their dominant arm, it really isn't obvious if one arm is more developed than the other, certainly not at a glance.
In one story, a man claimed an item of his had been stolen during a thunderstorm. The house was dark because the power was out. He was awoken by a thunderclap, then saw the burglar in the lightning flash that followed. E Brown knew that the man was lying (he had actually stolen his own property for the insurance money, then made up the story), since in real life, thunder follows lightning, not the other way around. Of course, it's inconceivable that there would be more than one lightning flash during the course of a thunderstorm.
A contest is held in which contestants complete a quiz for 3 secret prizes for 1st, 2nd and 3rd place. The first place winner receives the best prize: a watch, which he discovers has been broken. The theory of the crime is one of the contestants secretly examined the prizes and played with the watch and broke it. The culprit turns out to be the 2nd place girl that purposely missed a question she should have gotten right: "Name a word that has three double-letters." The girl referred to herself as a "bookkeeper". Assuming she remembered such a fact, the solution fails to prove why she threw the contest or definitively eliminate her from the suspect pool of the other contest losers.
She knew the (intact) second prize was worth more than the (damaged) first one.
One case was solved because the culprit claimed their wobbly table was knocked and various possessions spilled on the floor. EB points out that the table was three-legged, and that such tables can't tilt. Three-legged tables won't be wobbly even if the legs are different lengths. However, if the table was on a slant to begin with, jostling it might very well knock it over, or at least knock the items off.
At least one time the series used this trope absolutely correctly. Bugs claims to have been kidnapped at Encyclopedia's behest (how a 5th-grader was able to hire and control adult Mooks is never discussed). He describes being imprisoned in a small room, and attempts to escape by removing the pins from the door hinges, but they are on the other side of the door. Then he tries to wait to the side of the door and jump his kidnappers when they come in, but the door opens into his face, foiling the attack. Standard house doors cannot open away from their hinges, only toward them.
Encyclopedia Brown liked solutions where the answer hinged on an American city having the same name as a foreign place that was generally more famous, for example Paris, Texas. This isn't usually conviction by contradiction, but became a case of it bordering on Unfortunate Implications in the answer to one puzzle involving an American city called Palestine, where Encyclopedia declared that it had to be the American city because "nobody calls the real one Palestine anymore." Apparently in Encyclopedia Brown's world, Palestinians don't exist. note Current political controversies notwithstanding, prior to the 1967 War the non-existence of Palestine was indeed generally considered a non-controversial matter.
A boy gets injured in the foot by an unknown suspect. Another boy is asked to bring a spare shoe for the injured party. Brown deduces the other boy is the perp because he brought the right shoe for the injured foot without asking beforehand which shoe to bring. While common sense might suggest to the boy to think about which foot would need the shoe, he still had a 1 in 2 chance of getting the right shoe if it didn't occur to him right at that moment to ask and, although the wrong shoe might not fit comfortably, it could still fit his foot if the size allows for enough space.
A local con man claims to have bred chickens that can lay square eggs. He comes up with a lame handwave as to why he simply can't show them, and claims instead that he'll stage a publicity stunt by having the skydiver standing with him jump holding one in a box only to have it still intact afterwards but needs money for promotion. Encyclopedia calls him out because the skydiver is wearing only one parachute, and all jump with two in case one fails...because there's no chance that someone might wear something different to a publicity event than during actual skydiving. Granted the con man does describe his accomplice as dressed "ready to jump", but considering the whole absurdity of the situation (the convenient excuse as to why he can't just show the eggs, the fact that a square probably would be crushed if held by a skydiver anyway, why such a stunt would even be necessary to promote square eggs, and of course, what the hell besides novelty value is the benefit of square eggs anyway?) it seems kind of silly that Encyclopedia quibbles over such a minor technicality.
One story's suspect gives the alibi that she was in the shower at the time of the crime. During the "interrogation", she starts filing her fingernails, which Encyclopedia claims is proof of her guilt, saying that you never file wet nails because they're too brittle and will break rather than filing down evenly. The idea that the girl might have dried off after her shower apparently doesn't enter into his head...
The Swedish edition of The Phantom had a few pages of reader-submitted letters and material for a long time; one mainstay was various whodunnits, of course concocted by one of the readers. While some were well-written, far too many that hinged on the culprit making any kind of factual fallacy (such as stating that Canada's capital is Toronto) which immediately had them busted. The one that set off the trend was admittedly fairly good; someone disguised as a Muslim imam, who orders a ham sandwich...
One whodunnit was a murder taking place in Germany, and one suspect claimed to have been in the woods picking berries at the time, while the other said he had been at the movies seeing a Bond movie, and remarked on Bond's funny German accent. While the readers were supposed to suspect the latter (Bond is German?), certain little-known cultural traits were at work - movies are always dubbed over with German speech in Germany, whereas picking berries in wooded areas you don't own counts as theft and/or trespassing, in contrast to Swedish law which allows it. Although one has to wonder why a German person would remark on an accent being German. (If he thought it was a funny kind of German accent, that still wouldn't be the likely way of putting it.)
One early Supergirl comic featured a woman impersonating a man claiming to be Supergirl's husband-that-she-forgot-she-had, in order to make her (the woman's) boyfriend give up his crush on Supergirl. Supergirl saw through this at the beginning, because the woman put "his" arms around Supergirl's neck when "he" kissed her rather than around her waist, which is apparently something only girls do. Though she should be able to literally see through the disguise, beingSupergirl.
The first storyline in which Superman and Batman learned each other's secret identities (via Contrived Coincidence) featured Batman concluding that someone was lying about being an electrical engineer because he wasn't wearing rubber-soled shoes. On a holiday cruise. While a) Superman had X-ray-spotted a gun in the suspect's pocket and b) the guy did claim to have a job to do in a few minutes on the ship's generators, it's still rather jarring that "The World's Greatest Detective" apparently concluded that no-one can own more than one set of shoes.
If the above description is correct, there's another problem: an electrician is someone who works hands-on in electrical systems installation, maintenance, troubleshooting and repair; while an electrical engineer is usually someone who designs such systems but does not physically work on them.
Inverted in on story, of all places. When Betty is framed for academic plagiarism, Archie investigates the evidence against her and points out the flaws in it that prove her innocence. He then offers actual physical evidence that proves that she was framed by a jealous rival.
Inverted again in another story where Archie accidentally spills paint remover on an 1870 Frederick Church painting that Mr. Lodge buys from an art dealer. Mr. Lodge is predictably upset, but then Archie wipes away more paint and finds the signature "Picasso". Mr. Lodge is suddenly thrilled, thinking that he's actually discovered a long-lost painting by Pablo Picasso, but then his butler Smithers reminds him that Picasso was born after 1870, the date when Church supposedly painted his picture. When it dawns on Mr. Lodge that Church couldn't have painted over Picasso's original painting if Picasso wasn't even born yet, he realizes that he's being conned. Mr. Lodge then takes back his check from the crooked art dealer, and gets Smithers to help him literally throw the dealer out of the house.
Yet another story had Archie and Jughead housesitting for Mr. Lodge and Veronica while they went on a family trip. A crooked art dealer and one of Mr. Lodge's security guards use the opportunity to steal Mr. Lodge's collection of priceless paintings and replace them with forgeries, while trashing the Lodge house to make it look like Archie and Jughead threw a Wild Teen Party and distract Mr. Lodge. When he comes home, Mr. Lodge falls for it and is furious with Archie and Jughead, but then Archie realizes that the paintings weren't at all damaged by the "party". He convinces Mr. Lodge that they were hung after the wrecking was done, and proves that they're fakes. Archie and Jughead then direct the police to the art gallery, where they find Mr. Lodge's real paintings. Archie explains that the crooked art dealer couldn't bear to damage his expert forgeries and ended up tipping Archie off to the fact that they were fakes, which makes this a case of Hoist by His Own Petard.
Regularly parodied in Viz magazine's strip Spot the Clue, supposedly written by a different guest celebrity every month.
When Tim Westwood "wrote" the strip, the murderer gave himself away by referring to an album that hadn't been released at the time the strip was set.
When David Bellamy "wrote" the strip, the murderer revealed himself by giving a plant's botanical name in capital letters in his speech bubble.
When Hugh Scully "wrote" the strip, the thief claimed she had been cleaning an Edwardian bureau at the time of the theft, when the style of carving on the bureau clearly showed it be be from another period.
When Albert Camus "wrote" the strip, the murderer's lie was to say he enjoyed life, when in fact the inevitability of death renders everything we do meaningless and absurd.
When Alan Sugar "wrote" the strip, the murderer claimed to have sent a message on an Amstrad eMailer, forgetting that Amstrad eMailers are shit and never do what you want them to do.
Trixie Belden had several comic book stories. One involved a female suspect hiding out as a guy. The crook forgot that female shirts tend to button on the opposite side.
The Bruce Wayne: Fugitive arc toyed with this; every time one of the bat-family found some piece of evidence indicating Bruce had been framed for Vesper's murder, someone would pipe up with the obvious: Bruce was more than capable of forging/planting that very same evidence to make them think he'd been framed so no amount of forensic evidence would ever clear him in their eyes. Ultimately, they decide to have faith in his innocence based on their personal experiences with him and not solid evidence of it.
Played with in Dogma — Loki argues to Bartleby that a couple is adulterous because "No married man kisses his wife like that." Bartleby retorts that it's a good thing Loki's never had to serve on a jury. So Loki asks the couple. Hilarity Ensues.
In Inglourious Basterds, Hicox is doing a good job of staying undercover... until, rather suddenly, the German soldier he's been talking with says that he's given himself away. The audience is not told what the mistake was until much later: He used the British hand gesture for "three" (index, middle, and ring fingers raised) instead of the German one (thumb, index, and middle fingers raised). German audiences naturally pick up on it more easily, aided as well by the fact that the German character visibly reacts to it.
In two of the three endings to Clue, Wadsworth deduces that the cook used to work for Mrs. Peacock's, and that Mrs. Peacock had killed her, because Mrs. Peacock said that what the cook had made for dinner was one of her favorite recipes—"and monkey's brains, though popular in Cantonese cuisine, are not often to be found in Washington, D.C."
In The Final Cut, Robin Williams' character concludes that a man he sees in a recording is someone he met years earlier when they were boys, because he cleans his glasses on his shirt. Most people who wear glasses will clean them on their shirt if a more suitable cloth is not available.
Played with in A Few Good Men — a murder victim in Guantanamo Bay's military base in Cuba had supposedly received long-awaited transfer orders for a flight early the next morning, but had not packed by the time of his murder later that night nor called any friends or family back home to make preparations. When this is mentioned during a witness examination with the man issuing the transfer, intended to trick the witness into self-incrimination, the witness counters that he couldn't possibly explain the dead man's motives, not being the man in question. However, the contradiction is enough to irritate the witness and put him on the defensive - Justas planned.
Some examples from Donald J. Sobol (the Encyclopedia Brown author)'s less famous solve-it-yourself series for adults, Two Minute Mysteries, starring Detective (no first name given) Haledjian:
Haledjian knows someone is the culprit because he claims that a cook in the kitchen was yelling and waving a bright red lobster before he was found murdered. The lobster wasn't supposed to be cooked yet, and lobsters are only red when they're cooked. However, that detail wouldn't be impossible, just weird. The back cover of a regular mystery might well say something like, "Why was the cook waving an already-cooked lobster before he was killed?" Another question is, was the cook yelling because the lobster had already been cooked?
Haledjian knows that Nick the Nose, the informant, is lying (as he always is), because he claims that a dying Brazilian's last words were in Spanish, and the national language of Brazil is actually Portuguese. (Because the Brazilian couldn't be one of the many immigrants to Brazil from nearby Spanish-speaking countries. And because it would be impossible for a native Brazilian to speak his last words in a foreign language. And because it would be impossible for an Anglophone informant to simply mistake Portuguese for the extremely-similar-sounding and more commonly heard Spanish language.) In fact, depending on what he said, it could sound exactly the same in Spanish or Portuguese, especially from the mouth of a dying man (who presumably isn't speaking particularly clearly).
One of the cases involved the apparent suicide of an actor and Haledjian claiming that the note left behind was a fraud written by an English rival of the deceased because the note used "theatre" instead of "theater" and other British spellings. (Because apparently, Americans are only supposed to use American spellings. And no one ever uses "-re" to refer to stage productions and "-er" to refer to a local multiplex.)
This one is particularly egregious: most actors, even American ones, probably would spell it "theatre", unless they were specifically referring to a movie house. In fact, This Very Wiki uses "Theatre" as the namespace for plays, not "Theater".
Another case has Haledjian declaring someone's alibi faulty because the person identified the tune a band was playing as "God Save the Queen" rather than "My Country, 'Tis of Thee" (which has the exact same tune), and so knew about a British performing troupe being in town. Many American Gilbert and Sullivan companies play "God Save the Queen" before performances, and as a Standard Snippet, it's always "God Save the Queen." Even worse, the actual name of the tune is "National Anthem."
The alleged murderer claims to have not visited his friend for days, but is caught because he leapt over the freshly-painted stairs and knocked on the window set into the door rather than the freshly-painted door itself. (Because it's not like fresh paint looks and smells like fresh paint, especially fresh white paint. And because it's not like some people leap over stairs as a matter of course, or like knocking on a window is often simply louder than knocking on a heavy door.) This is one of the many cases that were recycled for Encyclopedia Brown to solve.
An English professor's suicide note is considered fraudulent and a product of foul play because it contains a split infinitive. (Because English professors always follow grammatical rules, even when distraught and suicidal, and all English professors accept "don't split infinitives in English" as a rule.)
A variation on this has actually happened in real life. An old, very cultured, French widow was found murdered in her villa, with a note on the wall in blood that implicated her gardener. However, it said (in French), "Omar m'a tuer" ("Omar to kill me") instead of the grammatically proper and phonetically identical "Omar m'a tué" ("Omar killed me."). They still haven't solved the case.
One also has to wonder why a dying person, writing in their own blood, would bother to write more than 'Omar'. Why not throw in the murder weapon, time of the event, and description of the room while you're at it? "Omar killed Me in the Villa with..."
An inversion of that was actually used as a clue in the book Something Wicked by Alan Gratz. The name of the victim's son, Malcolm, is found written in blood next to the body... except everyone, including the victim, called his son Mal, and why bother with the extra four letters if you're dying and the first three are sufficient?
A situation that was almost exactly the same cropped up in one of Jim Sukach's Dr. Quicksolve books. The suicide note said "if I were him" instead of "if I were he".
Similarly, in an Encyclopedia Brown case, a note about who was supposed to receive some calendars couldn't have been written by a math teacher because it says "divide the calendars by 1/2", which would actually be multiplying by 2, because math teachers never make mistakes in grammar or use common English-language phrasing fallacies outside of the context of the classroom.
Haledjian also dealt with the rather more plausible inversion, where the suicide note was in perfect grammatical English despite the dead man being an uneducated Italian immigrant who read the news in an Italian-language newspaper.
A similar situation occurs in A Series of Unfortunate Events. Grammar Nazi Aunt Josephine's alleged suicide note contains several grammatical errors, leading the Baudelaire siblings to believe it is a forgery. It turns out that the note was genuine, but the suicide was fake, and the errors were a coded message to that effect.
The suspect claims it is his first time in the victim's house, but when a doorbell rings, he knows to answer the back door. (Because nobody can hear where a given sound is coming from, and it's certainly not that front doors often always have a double ring (ding-dong) and back doors a single ring (ding). And because there's no way at all the suspect could be from, live in, or have lived in a town where it's customary to do everything at the back door except on special occasions.)
The painting's owner claimed to be getting dressed to investigate the disturbance, with his right leg in his pants and his left leg out. (Everybody always gets dressed and undressed left-leg-first. Didn't you know that?)
A criminal's itinerary read "Palestine" instead of "Israel", thus revealing he wasn't actually going to the Middle East as his girlfriend claimed. (Not a lot of tolerance for potential political differences.) Encyclopedia Brown got this one too. His dealt with a list of international locations which turned out to be cities in Texas, and "Palestine" was the clue.
Ironically, a better inconsistency that wasn't part of the solution but was instead mentioned earlier by Mrs. Brown was that the list mostly had individual cities (London, Paris, Odessa, etc) but didn't list a specific city in Palestine.
Sobol really really liked making the solution hinge on phrasings that can be either of two different sets of words, in both Encyclopedia Brown and 2-Minute Mysteries.
"An arrow flight away"/"A narrow flight away": The detective was specifically looking at the flight of stairs when he said it and the suspect still replied "then why don't you go outside and look for it?", rather than "upstairs", revealing that he knew that the stolen diamond had been shot out of the house with a bow and arrow.
"Flawless"/"floorless" The police have confiscated a car whose floorboard was used to smuggle drugs. Haledjian is trying to catch the crooks by posing as car salesman "Flawless Phil". He mentions to one prospective buyer that "the interior is floorless"; when the buyer walks away, Haledjian orders him arrested on the grounds that had he been innocent, he would have heard "floorless" as "flawless", the slogan of the lot. While there are accents that make 'flawless' and 'floorless' sound similar or even the same, there are many more where they are quite distinct. And in either case, isn't it possible that the guy just didn't like the car or perhaps he had to take a dump? (In this case the guy didn't help his case by acting really nervous.)
Two Minute Mysteries also recycled the "Frisco" clue discussed in the Encyclopedia Brown section above.
In one of the Two-Minute Mysteries, the suspect was caught after Haledjian said the (diamond?) was hidden in the cupola because the murderer was the only one who ran up towards the attic instead of to the kitchen. Because only a murderer could know that a cupola (usually "KOOP-ul'uh", but the pronunciation varies by person enough that "kupp-ola" wouldn't be suspicious) was a term for the little domed thing on top of the house and not just an annoying term for a cappuccino maker, that only someone who had killed the house's occupant would assume that the stairs going up lead to the roof level, and that it's impossible to see a cupola from outside the house.
In one case, the question of whether or not a ring bearing a very valuable diamond was stolen or legally bequeathed comes down to the accusing party's testimony. She says that when she saw the deceased for the last time (when he supposedly bequeathed it to her), he was reading a book and wearing the ring on his right hand, so when he turned a page the sapphire flashed brilliantly. Haledjian figures that the 'witness' is lying because the dead man was reading a book written in Hebrew before he died- and Hebrew is written right to left. The man would have been turning the left page with his left hand, not the right page with his right hand... But most people turn the page with their dominant hand, regardless of direction. If Haledjian had been correct here, then people would use a different hand to flip back through a book than to flip forward through it. Even animators knew this wasn't true.
Overall, though, this series tends to deal with it in a better way than Encyclopedia Brown, in that the stories are SO short that Haledjian only has time to declare that he believes the suspect is lying, not necessarily guilty.
Sometimes, Haledjian completely disregards sheer stupidity as an answer. In one mystery, he was on his way to a BBQ when the host was found murdered. His neighbor came over, saying he heard his wife scream in horror, and during the interrogation, spotted the wife's pearl earring in the grill and reached his hand in to retrieve it. The detective told him that he obviously planted the earring because, despite having just arrived, he knew that the coals were cool enough to plunge his hand into them. Apart from the fact that coal visibly whitens when heated and that people can sense heat when standing next to hot coals, does he ever consider the fact that the guy could have just been an idiot?
In one case, the head of an orchestra had two skilled violinists and had to decide which would play a solo on opening night. He picks A about five minutes before the performance is meant to start. When he goes to get A, he finds A has been killed, and then has to pick B. Haledjian decides that it must have been B who did it, because B walked onto the stage, sat down and began to play, when he should have tuned his violin and rosined his bow first. Like it's totally unthinkable that someone with an equal chance of getting a part would get themselves ready to play it, especially if the choice wasn't going to be made until about five minutes before it was meant to begin.
In one, Inspector Winters asks for bicarbonate of soda for an upset stomach while in a bakery. The baker says she doesn't have any; this leads the detective to deduce that the bakery must be a front for smuggling, since bicarbonate of soda is baking soda and no real bakery would be without it. Except there's the possibility that the baker was unfamiliar with an antiquated term for baking soda (even more egregious today than when it was originally written: many modern chemists might find the term unfamiliar, since the proper scientific terminology has been "sodium hydrogen carbonate" for decades, and was "sodium bicarbonate" rather than "bicarbonate of soda" for some time before that).
There was one book of "Solve it yourself mysteries" intended for kids which seemed to do something with the trope while inverting it with more common examples. (e.g. saying a nurse was likely sending threatening calls because there were babies screaming in the background, puzzles about time zones ) One case involved "I was woken up by thunder and then saw a man stabbed during the lightning" because lightning always comes before thunder. Yeah, makes sense, but apparently, there was only one strike of lightning.
Another case from the book had a murder take place at a country club wherein someone was pushed down a hill and broke his neck in the fall. The tennis player who reported it was apparently the murderer because he had a grass stain on his shoes and of course, tennis players would have different shoes for tennis than walking around in the grass. Yeah, you'd have a point there, since many tennis players keep a separate pair of shoes specifically for Tennis the way people do for a lot of sports, but apparently, the grass stains certainlycouldn't have come when he ran over to see if the victim was okay or not. (In real life, it'd have been more suspicious if he stopped to change his shoes like the detective thought he would.)
Another one had a victim killed by having a heavy clock dropped on his head, and there were two murderers. All three suspects claim it was most likely an accident. Person #1's alibi was that he was watching a TV show at the time of the murder. Person #2 hears something fall to the floor from down the hall and runs to investigate, and person #3 was out smoking, then walked in and simply found #1 and #2 standing over the body. The detective says that Person #1 and #2 are guilty for several reasons. One, the clock stopped at 8:51 and no TV show ends at 8:51. This is an analog clock (the stories were written in the 70s) and evidently, there's not the possibility that it might have been simply running slowly (or that the clock's hands got jarred by the impact). The second one also apparently couldn't have heard the body from the other side of the hall, but it's actually not impossible to hear something heavy fall to the floor, especially if it's a clock heavy enough to kill someone.
Lampshaded in one story where the detective is listening to someone's testimony on a crime, and mentions it won't stand up in court because he was telling the story as he saw it, through the mirror of a car.
Isaac Asimovlampshaded this in one of his stories, in which a character points out that in most detective stories all the detective's deductions could easily be picked apart by a competent defense lawyer and it's a good thing the detective is always able to use their deductions to make the perpetrator panic and incriminate themselves before they go to trial. That didn't stop him from flirting with the trope himself, though.
In one Isaac Asimov short story, two similar-looking girls work in a library. One of them murders the other, but claims she has an alibi — she was accepting a book return from a student at a certain point before the murder. The Sherlock determines that she was lying, and in fact the other librarian accepted the book, because the murderer didn't remember the name of someone who returned a book. He shared a name with the author of a book very well known to any librarian in that university. Not much evidence, but since she confesses later, that's what would matter in court.
It wasn't just a locally well-known author, but the author of THE chemical reference, period. A professional chemistry librarian could no more forget the name "Beilstein" any more than a conductor could forget an applicant named "Ludwig van Beethoven".
Unless she was distracted, or just not particularly amused by the coincidence (however, since an emphasis is made on the girl smiling at hearing the name, both can be argued against). A Black Widowers story, "Spell It!", removes this possibility by having the man make a huge deal about his name being famous after a bookstore clerk innocently asks him to spell it. Of course, this version discounts the fact that two different people may spell similar-sounding names differently, thus leading a clerk to always double-check. This was a Black Widowers story, so the solution wasn't claimed as definitive — see below.
Asimov wrote a whole slew of anthologies in the Encyclopedia Brown vein, wherein the members of a men's club would discuss various mysteries during their monthly dinner at their favourite restaurant, until their waiter provided them with a solution. His use was usually more justified, as, not adhering particularly strictly to the Encyclopedia Brown formula, the Black Widowers were usually pursuing a problem purely as an intellectual exercise, and more often than not, their goal was not to find a legally substantial argument, but just to construct any explanation that was entirely plausible and fit all the facts. (For example, one of the "cases" they tackle is to work out the subject matter of Professor Moriarty's doctoral thesis.)
One of those stories inverted this trope by having the shaky evidence (that an accountant would associate the phrase "half past eight" with 8:50 since "eight and a half dollars" is $8.50 and accountants are marinated in money) given to a defense lawyer with an innocent client, so that he can use it to impeach an otherwise unshakable witness. The story was written at a time when digital clocks were still relatively new.
In the above story, "What Time Is It?", the characters admit that, while not conclusive evidence, this could be used by the guest, a defense attorney, to sow reasonable doubt in the minds of the jurors, allowing his client to be acquitted.
Questions like this were actually used to find spies, at least in the movies, but it was usually reversed — failure to know the National Anthem or last year's World Series champion was considered "evidence" of espionage. Asimov's joke was that spies who knew about that system would overprepare. In addition, Asimov had very strong feelings about the song, and considered it a tragedy that Americans didn't know it. He also wrote an essay about the importance of all four verses.
Asimov had a habit of writing mysteries in which the detective is either an amateur or a professional outside of his jurisdiction, so that he has no legal weight behind his investigation. The detective has a Eureka and figures out whodunit, but the only way to convince the real authorities to even arrest the criminal is to resort to Perp Sweating. The novels Murder at the ABA, The Naked Sun, A Whiff of Death (aka The Death Dealers) and The Robots of Dawn all fall into this pattern. Darius Just, the hero of Murder at the ABA, makes a point of saying that his deductions were all founded on circumstantial evidence and a defense attorney would never have let his argument stand.
In one of Asimov's short mystery stories, the culprit is a Québécois person using a false identity of an American. The detective tricks him into revealing his true identity by asking him to write the word "Montréal", and he writes it with an accent aigu on the e, whereas someone who only spoke English wouldn't spell it that way. To rule out innocent explanations for this information, the interrogator establishes by prior questioning that the American identity doesn't speak a word of French.
Justified in his short story The Singing Bell: the evidence against the culprit would never stand in court, but the detective explicitly states that he's just looking for enough evidence to convince a judge that a mind probe is justified. This can, by law, only be done to a particular individual one time in their life, so it's only performed for very serious crimes (like murder) when there's very good reason to suspect the accused is guilty, but not enough evidence to actually convict them.
In another short story, The Dying Night, featuring the same amateur detective, he is able to figure out who the killer is not only through very circumstantial evidence, but one which wouldn't even work today due to Science Marches On. In this story, the victim was killed because he had discovered the secret behind teleportation, and the killer wanted it for himself. When they entered the bedroom of the victim, everyone sees the sun shining through a window. One of the suspects, who had spent the last 10 years living on Mercury, leaps to the window in apparent fright, and spots the exposed film containing the information on teleportation. The detective surmises that he is the killer, since only he would hide exposed film out a window at night, forgetting that the sun would eventually rise. At the time the story was written, it was believed that Mercury always had the same half facing the sun. Asimov admitted the gaping plot hole this created in his story, but since the discovery had been made long after the story was published, he didn't see any point in trying to fix it at that point.
Ironically, while Mercury does rotate, it does so very slowly, meaning the story could actually work if the suspect just wasn't expecting dawn to come so soon rather than never.
A series of short plays for kids published in the UK featured a detective with the catchphrase "And I can prove it, because you made four silly mistakes". The mistakes rarely proved anything. (In fact, one of them was the fallacy namer for No True Scotsman; a character during the Jacobite Rebellion is exposed as an English spy because, amongst other things, he puts sugar on his porridge...)
One short story in the anthology Alfred Hitchcock's Sinister Spies is called "QL696.C9", by Anthony Boucher. It's about a librarian who was killed, leaving a the titular mysterious sequence of letters and numbers nearby. At the end of the story, the detective gathers the suspects in the, um, library in the traditional fashion, declares that the code was probably a library subject reference number, and starts to look it up. He's interrupted by the need to keep the murderer (a spy), from killing herself with the pistol she hid in her blouse. Turns out he knew it was her as soon as he figured out what the code was for, as the killer had the only name that was a noun, and the whole library scene was just to flush her out. Fridge Brilliance kicks in when you realize that the detective needed something from the suspect to avert this trope, since there's all sorts of perfectly good reasons a librarian would have to write down a Library of Congress reference code for swifts. Ironically, the anthology in question comes up when you search the LoC for the code.
Woody Allen, in one of his books, wrote a parody of the detective-catching-one-mistake trope (Match Wits with Inspector Ford). The situations and answers were all absurd. For instance, a kidnapping victim returns home by asking his kidnappers if he could go to a football game that he only had one ticket for. The detective figures out that he's in on it with the kidnappers, because his parents are in their 80s and he's 60 years old, and "nobody would kidnap a 60-year-old man, as it makes no sense."
John Dickson Carr specifically warns aspiring mystery writers about this kind of clue in his essay "The Greatest Game in the World." Of course, if you do what he advocates, having guilt depend on a series of clues rather than just one, you won't have that problem.
Uncle John's Bathroom Reader had a series of simple mysteries featuring Leslie Boies and her companion, Steve. In one story, Steve tells Leslie about a man whose life was saved because the night watchman at the factory he owned told him he dreamt the train he usually took was going to crash. So the man waited for a later train, and sure enough, his usual train crashed. Leslie comments that the watchman should be fired, because if he dreamt about the train, he must have been sleeping on the job. Because he couldn't have had the dream when he was back at home, clearly. This is a variant on the tale that actually introduces the element that makes this qualify; in other versions, the dreamer specifically states that he had the dream at a time when he was at work.
In one of the stories in Maurice Leblanc's Arsène Lupin book The Eight Strokes of the Clock, Lupin determines that one of the extras in a silent film is infatuated with the leading lady solely from the out-of-character lustful gazes he casts upon her in the film. (These days, we'd just call that "bad acting".)
In one of the original Miss Marple "Tuesday Night Club" stories, Miss Marple bases her conclusion on the fact that the gardener wasn't really a gardener, because he was working on Whit Monday. Justified Trope, because she's not trying to convict him, just solve the crime as a puzzle.
Discussed and then averted in the novel The Franchise Affair by Josephine Tey. The novel is about two women accused of kidnapping and enslaving a school girl and the attempts of their solicitor, Robert Blair to defend them. Midway through the novel, the womens' solicitor discovers a discrepancy that can be used to cast doubt on the girl's story (she could not have seen the view out of the attic window that she describes). However, Blair realises that a clever prosecution lawyer can argue around this and even if the women are let off on this evidence, the taint of the accusations will still hang over them.
Another juvenile book series titled You Be the Jury by Marvin Miller worked on this trope. You, the reader, were the jury and had to decide guilt or innocence based upon the case testimony and three pieces of evidence. In short, the defendant was guilty or innocent based on a contradiction within the testimony and evidence. One example was a case involving a radio DJ being kidnapped as revenge for publicizing the bad service of a local roofer. It turns out that the DJ faked the kidnapping as a publicity stunt as one piece of evidence was a photo of him after getting away from his kidnappers three days later. He was clean-shaven and the solution argues that he should have had a three-day beard.
Subverted in Death on the Way by Freeman Wills Crofts. The police prove that one of their suspects faked his alibi for the time of the murder, and consider that this is sufficient evidence to arrest him. It turns out he isn't the guilty party — when he realised he couldn't prove his innocence, he panicked and constructed a false alibi.
Occasionally Cracker falls victim to this trope, with profiler Fitz often using "Encyclopedia Brownisms" rather than genuine psychological insights. In one episode, he deduces that someone is the murderer, as they claimed to be a student and "you don't dress like a student" (because obviously, all students dress exactly the same way). In another episode, he not only deduces that someone is a closet gay, but also his alibis, because when questioned he said "I was at home with my girlfriend" rather than "I was at home with Lesley" — thus showing he was afraid of saying that his girlfriend's name was a potential man's name and letting Fitz think he was at home with a man (because, of course, everybody normally says "I was at home with [name]" to complete strangers, despite the stranger not having a clue who [name] would be).
In cases like these, it's hard to tell if Fitz actually deduces from these facts, or if he's got a hunch and is using some detail to prod (or, rather, bulldoze) a suspect's nerves. There are instances where his 'gotchas' are shown to be ineffective, immaterial or just plain wrong, and he merely forges on until he gets a hit. There is no denying his huge deductive leaps from small details, however.
Played for laughs in an episode of Blackadder Goes Forth: Blackadder reveals he discovered Nurse Fletcher Brown was a German spy when he asked her if her well-educated boyfriend had been to "one of the great universities: Oxford, Cambridge, or Hull. You failed to spot that only two of those are great Universities." To which General Melchett, a Cambridge man, replies, "That's right! Oxford's a complete dump!"
This was actually a playful poke between the actors; Stephen Fry (Melchett) is a Cambridge alumnus, while Rowan Atkinson (Blackadder) graduated from Oxford.
Not to mention, of course, that Hull University didn't even exist until 9 years after the end of WWI.
And, of course, it was eventually revealed the nurse was innocent (at least of passing on the information that made General Melchett suspicious in the first place), and the episode ends with Captain Darling scrambling to reveal it (just to make Blackadder look bad) as Blackadder tries to stop him.
She doesn't deny it at all, and pretty much confesses without actually saying she did it, giving all the traditional 'I thought you loved me' nonsense. So apparently she was also a German Spy?
In early episodes of Star Trek: Deep Space Nine, Dr. Bashir often mentioned the one mistake he made on his final Academy exam: he mistook a preganglionic fiber for a postganglionic nerve. This was all that kept him from graduating valedictorian. But in the episode "Distant Voices", an alien in Julian's brain points out what viewers with medical training (including writer Rob Wolfe's wife) caught right away — a preganglionic fiber and a postganglionic nerve are nothing alike. The alien accuses Julian of getting it wrong on purpose, which later proves to be true, though for a different reason. If Encyclopedia Brown had been security chief of Deep Space Nine, we might have learned about Bashir's Big Secret (he's genetically enhanced) four seasons sooner...
Also, there was an episode of Star Trek: The Next Generation where hearings were being held of Starfleet officers out of fear that there was a Romulan spy on board the Enterprise. One officer questioned was revealed to have falsified some personal information claiming he had a Vulcan grandfather, when the grandfather was actually Romulan. Everyone, particularly the witch-hunter who started the hearings, took that alone as just-about-proof that he was the spy they were searching for, but Picard recognized that it hardly counted and worked to get the hearings stopped.
One of the books had a Romulan spy hidden among the crew, and the "clue" that lead to his unveiling was that fact that "he separated his food into separate piles, so they did not touch, and ate them one pile at a time." It was explained that this was how Romulan children are trained. Of course, no other race in the universe could have that traditionnote though on the other hand it would be easy for a Federation computer to check if any of the supposed cultures of the people on-board have that tradition, with any discrepancy causing suspicion right up until it hits the other issue, or people who just don't like having their food mix on their plate.
Actually deconstructed in an episode of Star Trek: Voyager of all places. A copy of the Doctor finds himself in museum seven hundred years into the future, a museum dedicated to the "Voyager incident," which claims the ship caused an entire civilization to be conquered by another race. The Doctor tries to explain what actually happened, Voyager was just making a trade deal for for fuel that was misinterpreted to be trading for weapons. The Doctor could prove it wasn't Janeway who shot the first civilizations national hero, but an ambassador from the second race. However, it was pointed out proving who fired a single weapon in what circumstances doesn't really change the broad strokes of history the history they "oppressed" civilization wants to maintain. He does succeed in revealing the deception to the general population in the end, though.
In the first regular Columbo episode "Murder By the Book", the murderer, half of a mystery writing team, sneers that Columbo doesn't have anything concrete on him — just a motive, the fact that he took out a life insurance policy on the victim, the fact that someone else was murdered shortly afterward who he claimed not to know but in whose house was found a book with a personal autograph in it, and such odd behaviour as opening his mail shortly after finding a body on his lawn, and taking a large sum of money out of his bank account and putting it back the next day. And he's right, these things are all circumstantial evidence. Then Columbo points out that he found a vague story outline in the victim's office; apparently Columbo's (accurate) reconstruction of the murder matches one of the thousands of rough story ideas the victim had been scribbling down over the past couple of decades. The murderer immediately gives in, despite this being easily the weakest piece of evidence presented thus far.
Columbo's suspicions are often piqued by this sort of clue, and he always opens his investigation by giving his suspect an opportunity to provide a perfectly reasonable explanation for it. Several "Just one more thing"s later he's backed his suspect into a corner that he can't wiggle out of.
The worst part of the episode, though, is that Columbo finds the minor flaws in the alibi but misses what should have been a fatal flaw in the killer's plan — the police identify that the killer's phone placed a call to the victim's wife, but they fail to look at the time of the call and realize that it was the phone call where she heard her husband get shot, and not the call that the killer had placed to her house (from another phone) ten minutes or more before the murder.
An episode of House ("The Tyrant") has House confront Wilson's neighbor, an amputee who claims to have lost his arm in Vietnam. House deduces from various clues that the man is a veteran of the Canadian Army, and calls him out as a fraud — except to be told that although Canada didn't take part in the Vietnam War, they did send troops to Vietnam to enforce the Paris Peace Accords, which is how he lost his arm in a landmine incident.
Murder, She Wrote usually avoids this trope. One of Jessica's most common lines after a Eureka Moment is "I think I know who the killer is. The only problem is, how to prove it…?" Not so much in Season 5. (Coincidentally or not, these are the first eps after the 1988 writers' strike.) They had several eps where the guilty party knew something that anyone might have guessed. Case in point: In "Smooth Operators", the murderer knew that a bum was using a newspaper as a blanket.
Many episodes of Monk have Monk using this kind of evidence to determine the murderer from the start. The rest of the show is trying to get proper evidence, as well as motive and method.
For example, in "Mr. Monk and the Birds and the Bees", sports agent Rob Sherman has made it look like he shot and killed a burglar who apparently broke into his house and killed his wife (the trick is that he shot the "burglar" with a semi-automatic and the wife with a revolver, then planted the revolver on the "burglar", making great use of a Deceased Fall-Guy Gambit). Monk suspects Sherman is lying because he gave the alleged invader one single shot, instead of unloading his gun on him in a fit of rage and fear like someone would do in a situation like that. Further evidence is that the "burglar" owned a .22 caliber (which he left at home), the revolver found on the body was a .38 caliber, and there is no .38 caliber ammunition in his apartment.
At least in that instance, the suspect did indeed kill the guy and challenging his version of events would indicate murder. In "Mr. Monk Goes Back to School," Monk zeroes on science teacher Derek Philby for no other reason than he found evidence he hid his wedding ring in his wallet—which meant he was having an affair and lying about it, making him suspect number one in the death of another teacher whom the police assumed (and Monk couldn't prove otherwise) committed suicide. (Although this and the previous entry could possibly be explained by Monk's feelings for his own murdered wife.)
Note that Philby is a science teacher, so presumably he teaches labs as well as lectures. For many lab activities, wearing jewelry isn't safe or appropriate; although a wedding ring is unlikely to hinder its wearer's handling of chemicals or dissection tools, a teacher might well remove it to set a good example of laboratory dress codes in front of his students.
In "Mr. Monk Goes to Vegas," Stottlemeyer gets to be a Drunken Master when he realizes he solves a murder made to look like an elevator accident because of a contradiction in two tabloid photos, namely, the fact that the earrings the victim was wearing when she was getting onto the elevator were not the earrings that were found on the body when the elevator stopped, proving that a Body Double was present in the first photo.
In another episode, Natalie's parents talk about a couple of friends of theirs who died in a car accident. When Monk hears that the car involved was a British Morgan, he becomes suspicious because the British drive on the left, and this doesn't square with the positions of the bodies at the scene. Apparently, Monk doesn't know that most British car manufacturers, including Morgan, make left-hand-drive versions of their cars for countries that drive on the right.
What's more, it really beggars belief that the crime scene investigators, who had the car and the bodies right in front of them, failed to notice this. The Police Are Useless.
Psych: This is entirely how Shawn Spencer works. He figures out who did, and in some cases, how, then has to prove the why.
Of course, the whole point of the show is that he actually claims to have received the information from his psychic powers. Instead of "This spot on your shoe proves you did it", it's more a case of "I can sense that you did it, oh and here's a spot on your shoe that backs me up." Whether this makes a difference to the juries in this show's universe is unknown.
The fact that he has to point out the actual clues in order to get the cops to believe him in the first place indicates that yes, the evidence is what matters. Shawn's visions are pretty obviously not part of the legal proceedings, they're just the mechanism by which the cops find the hard evidence they need to prosecute.
It was mentioned in an episode that they have something like an 85% conviction rate for cases they're involved in.
Shows up quite a lot in Jonathan Creek (which was originally conceived as a British Columbo, after all). For example, from the fact that a piece of film supposedly secretly filmed by a stalker from over a tall fence used a pan instead of moving sideways, he deduced that it was taken by a short man standing on a box, and as the subject's manager was a short man, therefore it must have been him.
They sometimes try to justify this by having him say something like "I don't know, it could be just a coincidence, but..." and wait for this to intimidate the accused to blurt outmore definitive proof.
Shelby once identified a kidnapping suspect by breaking his alibi; he'd claimed he was at the movies around 8 or so but his ticket stub was for a 5:15. The suspect got irritated that she was going through his things and it was pointed out the evidence was not sufficient to point to his guilt—then he's identified based on his strange habit of drumming his fingers on his briefcase, making the same drumming sound as heard over the kidnapper's ransom call.
Another ep had Shelby try to identify a suspect in a smuggling case by the sound of his whistling a particular tune. She told Da Chief it had to be the musician who performed a concert in town whose song the suspect was whistling; Da Chief points out that a lot of people attended that concert and would have found the song catchy. A guy whistling that same tune walks past them and Da Chief smugly points and goes "See"?.
In Seven Days, there is an episode where some woman named Delores threatens over the phone to cause catastrophes unless Frank does as she says. Each time he performs a task, she answers a question. One of the question was about who won a certain year's sports championship. She answers correctly - this proves she's really a man impersonating a woman since Delores claims to know Frank personally and Frank has not known any woman who could correctly answer that question. The other possibility is "she" was either lying or delusional about her connection to Frank. Incidentally, this turns out to be true: Dean Loris doesn't know Frank; he was a homicidal disgruntled ex-NSA employee jealous that he wouldn't get to be the first Chrononaut and wanted to humiliate Frank for doing what he never got the chance to do..
On CSI: Crime Scene Investigation, Brass once grew suspicious of a grieving husband saying "I loved my wife" shortly after her death. A relatively minor example as he still has to get the lab to find proof before he could do anything substantial and the criminal wasn't arrested by the end of the episode (though the raised suspicions were enough for the wife's life insurance company to repossess the husband's newly-bought Ferrari).
In another episode, while searching the house where the female victim of the week lived alone, Sara dramatically announces "the toilet seat is up - a man was here!"... without even entering the bathroom to check if maybe the victim had been vomiting in the toilet (they'd just found a lot of spoiled food in the fridge, after all), or whether she'd been interrupted in the middle of cleaning the bathroom, etc.
Criminal Minds: Almost every profile, leading to several false arrests following generic descriptions. This is why profiles are not admissible in court for many jurisdictions. Most episodes end with perp sweating for confessions or real evidence to get around this. The truly strange thing is that even though they are fully aware their generic descriptions are often very wrong to start with, they get extremely annoyed should someone cast doubt when they make a prediction.
Hotch actually says in one episode that the team's only job is to win an arrest- whether or not they've gathered enough evidence is "for the courts to decide". Considering the standards for an arrest can be as flimsy as a contradiction in the story, the team practically lives on this trope.
Occasionally played with in the show, such as in "Doubt". The guy they arrest is obviously the killer, but he doesn't confess and they have no real evidence against him besides the profile, so they're forced to let him go (the fact that a Copy Cat Killer attacks while he's in custody helped).
The team will often catch the perpetrator in the act of attacking their latest victim, thus enabling the real evidence to fall into their lap. The catch is that some episodes will point out how they don't have enough evidence for a warrant and need a pretext to bust into the suspect's property but in most cases, the mere identification of the most likely perpetrator cuts to a scene in which SWAT is breaking down their door.
Another ep had the profile as the primary evidence against an amnesiac suspect since they caught him at his home and not in the middle of trying to kill his latest victim as per the usual formula. Lucky for them the suspect regained his memory and led them to another one of his undiscovered victims.
Law & Order: Criminal Intent: Detective Goren's entire Modus Operandi is coming up with contradictions to the suspect's story and using them to get the suspect to confess, often with their lawyer fully present. Like its predecessors, the suspect often gets so upset they decide to confess over their lawyer's objections.
There's also the episode where a suspect, a substitute teacher, says he hasn't been to Egypt and learned about the new Library of Alexandria from a magazine article. When the suspect says that the library has state-of-the-art smoke detectors and Goren didn't see that detail in the magazine article, that the guy was lying becomes a major plot point. An arguably more likely explanation, that the substitute teacher was making a lame joke about the fact that the old Library of Alexandria burned down, isn't even considered.
On Law & Order, when the police use contradictions in a suspect's story to solve the case for real, they're smart enough to use the it to gather more evidence to confirm the suspect's guilt.
One exception was in "Savior": a teenager claims she tried to lift some family jewelry for her boyfriend but when the jewels were missing, he shot her and her mother in a rage. The DA points out she could have stolen the jewelry herself without inviting her boyfriend into the house and concludes instead that she was paying the boyfriend the jewelry to murder her mother and he shot her when the jewelry was missing.
ADA Claire Kincaid once suspected a wife of the murder the husband had just been found guilty of. Her reasoning was that in a pretrial interview, the wife tried to cover for her husband's bank account withdrawals (which the victim was blackmailing him for) with a sloppily-crafted alibi. On the witness stand during cross-examination, she stuck to the same obvious lie with no elaboration; having known ahead of time the DA would ask about the money, she had more than enough time to come up with a more plausible explanation.
In another episode, a husband's conviction for the murder of his wife hinged on the theory he stole a brooch from her body the police later found with his mother. The defense brings in identical brooches to challenge the DA to prove the one they have is the right one. The victim's lover identifies the brooch from an engraving she'd made on the back of it.
In one episode, Cerreta and Logan interview a murder victim's family, and the son tells them that his mother wouldn't have killed his father, saying that he was with her at the time of the murder. Later in the episode, Cerreta wonders why the son didn't say she didn't kill his father, if they were together. Although the variation, while still a leap on the part of the detectives, is rather significant in that if someone is physically with you at the time of a murder, you know full well they couldn't have done it and thus have little reason to prevaricate.
Assuming, of course, that all the statements are logically interconnected, and the son didn't actually mean "She wouldn't kill him, and she was with me, anyway, so it's moot." Traumatized families of murder victims aren't always speaking in the most logical thought progression, and it seems odd to take their minor verbal flubs as greatly significant.
A variation of the old "I'm innocent" vs. "You can't prove that" giveaway is used in an episode of The Mentalist when the main character sits down three suspects and declares that he's going to have them fingerprinted to see who accessed a certain company computer. Two of the suspects become visibly upset and protest that of course their fingerprints will be on it because it's a public terminal. The third suspect says, "Go ahead. It'll just prove that I'm innocent," which of course immediately arouses suspicion because only the culprit could know that their fingerprints won't be found.
Crownies features this when a teacher accused of having sex with a student claims that a note the student had in her possession was written to his wife years earlier. Conveniently, the note happens to mention a brand of alcopop that didn't exist at the time.
The spinoff, Janet King, has an inversion when Alex Moreno is on trial for sending a teenage girl he'd met online (actually an undercover cop) a text message asking her to perform a sex act. Moreno's defence is that he knew he was talking to an adult from the beginning. His reasoning? No real teenager talks about their parents in a chatroom without using some kind of chatspeak term. The judge accepts this and acquits him. And then turns out to be a pedophile himself, with a long history of corruption.
24: in the first season, Jack is interrogating a businessman in his limo, trying to prove he isn't who he says he is while connecting him with the conspirators in the day's events. His initial "contradictions" are fairly shaky, such as why is an honest businessman is meeting someone in a garage unless the person was a criminal. The real clincher that he's a phony is when he tries to attack Jack with a knife he keeps in a secret compartment of the limo; why would an ordinary businessman who can presumably afford security carry a blade in his car unless the guy he was meeting with was a criminal? Perhaps the guy's just Crazy-Prepared? In this case, it may have been as much about the knife itself as the fact that it was a specialized blade: a Microtech HALO that's something only a Knife Nut would procure.
One case from Mathnet on Square One TV involved a number of contradictions which made detectives Kate Monday and George Frankly suspicious of a kidnapping victim's involvement in the crime. In "The Problem of the Trojan Hamburger", amateur gem cutter Hans Ballpeen is kidnapped and the Despair Diamond is stolen afterwards. Ballpeen manages to escape and explains that he was forced to cut the diamond. Monday and Frankly are more than suspicious because of not one, but a number of contradictions in his account. First, Ballpeen was kidnapped first and then the diamond was stolen - it's reasoned that there's no point in kidnapping a gem cutter unless you have one to cut in the first place. Second, Ballpeen claimed he hadn't cut a diamond in years, which made the detectives wonder why someone that rusty would be kidnapped instead of someone more skilled. Third, Ballpeen doesn't identify the diamond as the Despair Diamond. That was considered odd since it was a world-famous diamond. Fourth, he claimed that he was released somewhere in the woods, hiked to a highway, and hitchhiked home. Kate Monday pointed out his boots were pristine and George Frankly reasons that anyone getting away from kidnappers would find first find a phone and call the police.
Many perps in Cold Case collapse and confess after being caught in a contradiction, no matter how petty, after having got away with it for decades.
Subverted on Murdoch Mysteries when a caravan of gypsies are accused of burglary by the sons of several upper-class families who've been robbed. Inspector Brackenreid initially arrests the gypsies, but he later smells a rat when he notices the holes in the boys' story. Instead of arresting them based on that, he sets up a sting that confirms the boys' own guilt.
Slylock Fox uses this trope in nearly every strip as Slylock's main way of crime solving.
The Comics Curmudgeon routinely speculates as to what kind of brutal police state the characters live in that allows Slylock to operate so capriciously and arrest people based on such flimsy cause (and in which he's sometimes shown not just as a detective but as the prosecuting lawyer in court).
Subverted on Calvin and Hobbes when Susie is hit with a flurry of snowballs. She goes after Calvin, who has a wheelbarrow with him, and who protests that Susie only has "circumstantial evidence." She clobbers him anyway, and while lying face down in the snow Calvin claims that "you can't get a fair trial in this town."
One episode of The Whistler featured a man who killed his wife and made it look like a suicide. The police investigation and interrogation, conducted in the wife's apartment, has some close calls, but it looks like he's gotten away with it. The detective rises and heads for the door, ready to close the book on the case...and the wife's alarm clock goes off. Why would someone who's planning to commit suicide set their alarm clock to wake them up? The detective comes back, and says it's time to restart the interrogation from the top, as the husband breaks down.
Parodied in John Finnemore's Souvenir Programme, in which the great detective John Finnemore deduces the maid is guilty of murder because she falsely claimed that "impossible" is a nine-letter word.
A popular (well, often seen) riddle for kids goes like this: The detective is in a hotel room because the hotel's director told him that a famous thief is in the hotel. Then, someone knocks at the door of the detective's room. He opens, and there's a guy, who apologizes: "Sorry, I thought this was my room." The detective arrests him immediately, and guess what, it's really the Gentleman Thief he was looking for. Oh, the reason? Because nobody will knock on the door of his own room - so the thief must've been checking whether the room was empty and he could plunder it! (Because it couldn't be, let's say, that his wife was in the room, had been taking a shower and he wanted to warn her, in case she wasn't dressed yet, and other people were in the corridor, or that he left the keys in the room while his wife stayed so he had to knock the doors. Guess the thief is at least guilty of not inventing a good excuse.)
Another riddle involves the murder of a wealthy man who is killed on a Sunday. Upon being questioned, all of the servants give various alibis: "I was polishing the silver," "I was mowing the grass," etc. The "killer" is the one who claims to have been checking the mail, because mail isn't delivered on Sundays—because apparently, it's impossible to forget that and just check every day out of habit. Or to have forgotten to check on Saturday, and instead get the mail the next day. Or to receive a newspaper that is delivered on Sunday. Or to get mail delivered by others than the Postal Service (how uncommon this is may vary between countries).
Especially erroneous in the US, since the USPS will deliver letters on Sunday for an extra charge,
Yet another one had a woman who was attacked on the walkway leading up to her house, then the robbers tied her and her family up while robbing the place; the detective, arriving an hour later, noticed his long shadow in front of him on the same path and insisted that she was in on the robbery because she hadn't noticed her attacker's shadows behind her. Because it's not like the angle of the sun would have changed, or she simply hadn't noticed . . .
In The Crucible by Arthur Miller, Sarah Osbourne is suspected of witchcraft because she muttered something after being refused alms when begging. She claims she was just reciting the Commandments, but she cannot recite them for the court and is thus convicted. This is in keeping with the overall point of the work, which is that the trials are inherently unfair and the 'evidence' is flimsy and being twisted by hysteria and malice.
The first Knights of the Old Republic had a sidequest on Dantooine in which you determine which of two suspects is the murderer by poking holes in their testimonies. During the first round of questions, you find out that one of the two suspects lied, but he's not the murderer and it wouldn't do him justice to accuse him just based on this evidence — the truth is more complicated and can only be found out by repeatedly questioning both suspects and the forensic droid. You can also bypass the whole "logic" aspect and say that you know who did it and that your reasoning is that "fat people always lie."
Mass Effect 2 has a sidequest where Shepard must use various fragments of messages to identify which of five possibilities is the Shadow Broker's chief agent on Ilium. The solution comes down to the use of a single contradictory pronoun to give the answer -'none of the above'. Of course you are working for Liara, not the courts, and she's no longer too hung up on the whole 'reasonable doubt' thing.
Of course, she also summons Nyxeris to her office, where it is implied Nyxeris made the first move after being told she was guilty.
The DOS Edutainment Game, Eagle Eye Mysteries falls victim to this at least once. Although the guilty party usually tells a very blatant lie that makes everything they say untrustworthy, you usually find other physical evidence too. Not so in one case, where a suspected Moon rock theft hinges almost entirely on the thief calling said object a sedimentary rock, despite the player researching in-game that it is physically impossible for a Moon rock to be sedimentary. No other evidence is found to implicate the suspect. (Because if you don't know your basic geology terms, you are clearly a thief.)
Averted in the Ace Attorney series. The core mechanic of the game is to find and expose contradictions in witness testimony by presenting evidence. However, at no point is anyone ever proved guilty by a single contradiction alone. Instead, the objective is to expose a contradiction, which will then be covered up by a new, weaker story which can also be contradicted, and so on and so forth until the actual perpetrator's guilt is confirmed. The end result is that Phoenix and Apollo always need to present a pretty extensive case and put forth quite a bit of evidence before the court even considers believing them.
This is straight said to be an impossible act in the fourth game, when Apollo is accusing someone of being the real killer. Even though he's presented a pretty convincing case with quite a bit of evidence to back it up, and pointed out a load of contradictions in the witness's testimony, he's still unable to get them for the murder, due to not having any evidence that actually links them directly to the crime. Apollo does eventually get him by forcing a confession out of them.
Phoenix is also a defense attorney and his client is always the one on trial, so pointing out the contradictions is actually perfectly valid when the point is to create doubt in the testimony of those accusing your client. Also, it's suggested that the real perpetrators have to undergo another trial at a later date, so even when Phoenix exposes evidence against them they aren't necessarily convicted immediately. However, this isn't to state that the games don't use spurious evidence to advance the cases sometimes, nor that contradictions in testimony aren't sometimes given more weight as points of suspicion than they probably should be.
In the 1st Degree plays with this trope. While the prosecutor is required to poke holes in Tobin's testimony in order to get first-degree murder, it could be argued that Granger achieved it because Tobin had a total meltdown right there in the courtroom and revealed to much information.
Subverted in the Safe ending of Nine Hours, Nine Persons, Nine Doors. Junpei performs an epic set-up to reveal that Ace has prosopagnosia and can't tell the difference between faces, and thus killed Snake. Ace points out that his having prosopagnosia is true, but it in no way indicates that he was a murderer, and that he just kept it a secret because he was upset by it. Junpei agrees with this, and then says that the prosopagnosia reveal was just a springboard to lead to evidence that did implicate Ace in Snake's murder.
The Perplex City card "Alibi" pegs the maid as a murderer because she said she was getting the mail at the time of the crime - a Sunday. (Of course, no one ever picks up Saturday's mail on Sunday.)
Parodied in Moral Orel, in which Orel starts a detective agency. There are two suspects when the contents of Reverend Putty's collection basket is stolen: Joe the Devil in Plain Sight, and a clearly-innocent Susie. Orel ignores the expensive ice cream Joe has bought, and the fact Susie wasn't even in church at the time, and bases his conclusions on which Commandments they broke (or didn't break): Joe honored the Commandment about keeping the Sabbath Holy by refusing to cut his grandfather's lawn, while Susie broke the Commandment of honoring her parents by volunteering at a retirement center instead of going to church like she was told. If she broke one Commandment, then surely she would be the sort of person to break "Thou shalt not steal".
Double Subversion in Beavis and Butt-Head, of all shows. When our heroes are accused of egging Tom Anderson's house, Butt-Head is inspired by a court reporter he saw on TV to try and discredit Anderson's testimony by pointing out that Anderson couldn't clearly identify who threw the rotten eggs at his house. The judge is about to dismiss the case when the prosecutor objects, stating that neither Anderson nor any of the police reports or court documents had ever said the eggs were rotten. He then asks how Butt-Head could have known the eggs were rotten unless he and Beavis were the ones that threw them. Butt-Head has no response, and he and Beavis are sentenced to 500 hours of community service.
Rugrats had an episode like this. Angelica has Tommy hold a trial to find out who broke his favorite lamp, with Angelica as a persecutor. She attempts to finger Phil, Lil and Chuckie as the "poopatrator", but all of them have solid alibis. It isn't until Tommy realizes something random Angelica taking a nap - he said that she took one earlier and her introduction earlier in the episode had her obviously faking a wake up but was considered throw away that makes the babies realize that it would have been impossible for her to know what exactly they were doing and thinking unless she was there, which she was.
In "Krusty Gets Busted", the first Sideshow Bob episode of The Simpsons, Bart and Lisa's investigation basically comes down to this. First Lisa realises that Krusty wouldn't have used the Kwik-E-Mart microwave because he has a pacemaker, then that he couldn't have been reading the Springfield Review of Books at the magazine rack because he can't read. When Bart brings these points up on Sideshow Bob's show, Bob argued that Krusty wasn't one to follow medical warnings, and didn't need to be able to read to enjoy the Springfield Review of Books, thanks to the cartoons. Finally, in a Eureka Moment, Bart remembers that Homer stepped on the ends of fake Krusty's long shoes, causing him to exclaim in pain. Although Krusty usually wears oversized shoes, his feet don't fill them, so he wouldn't have felt a thing; Sideshow Bob, however, has feet long enough to fill the shoes.
An episode of The Raccoons titled "Simon Says" involves an aardvark claiming to be Cyril Sneer's long lost brother, Simon, who wants his share of the Sneer fortune. Simon claims to have been trapped on a desert island for a long time and eventually built a boat to get himself off the island. Bert however is suspicious and spends the episode trying to expose Simon as a fraud. Bert succeeds and when asked what made him wary, it's explained that during their initial handshake, Bert noticed Simon's hands were very smooth. If he had worked on building his own boat, his hands should have been rough and callused.
This is one of the reasons you're never supposed to talk to police officers unless there's a lawyer present. It's quite easy to say something that could be misconstrued as suspicious or incriminating, and police in Real Life are more diligent than in fiction about using holes in a person's statement as a starting point to single out the suspect(s) who will be investigated more thoroughly via obtaining warrants and gather the real evidence that's used in a conviction. When the police tell you anything you say "can and will" be used against you they aren't kidding. Conventional legal wisdom is to invoke your right to an attorney and never speakto police officers if you think the police suspect you of a crime. The lawyer is there as a witness.
Police are also more experienced and versed at some of the less well-known cues for discerning between how an innocent person vs. a guilty one will react to being accused of a misdeed and what would constitute suspicious behavior/language:
An innocent person accused will deny it, while a guilty person might make a statement that doesn't depend on actual innocence, such as "You can't prove that!" As pointing out that the accusation is by contradiction rather than evidence is closer to the second reaction than the first, it's not unreasonable for lampshading this trope to trigger a (further) investigation.
However, trying to tell truth or falsehood by someone's behaviors like this is questionably useful at best. One study suggested that training to detect these sort of details did not increase accuracy in detecting truth or falsehood, and in fact the longer a cop did his job the *worse* he became at determining truth from falsehood. This has lead to people ending up in jail due to not being shocked enough, or too shocked, about a death. The reason behind this is simple: when you focus too much on behavior to tell if someone is lying, you stop focusing on the best way to tell — their story simply doesn't add up.
Also, the "found out as a foreign spy because—" examples are very much Truth in Television if for no other reason than if you're found out as a spy, you're less likely to end up in front of a jury in a public court with all those pesky "standards of proof" and more likely to end up in a dark hole in a location known to no one with the government of the host country giving you some harsh interrogation, and pointing out the holes in their evidence is most certainly going to fall on deaf ears.
Though obviously easy to take too far, espionage is at least as much a national-defense issue as a criminal issue, and the primary purpose of interrogating spies is not getting a conviction, it's finding out A) what they've found out and B) how many other spies are in your country, and if possible, who they are.
For that matter, in the "found out as a spy/impostor" cases, there would usually be plenty of other evidence about the person having engaged in espionage/not being who or what they claim to be; the contradiction is simply the first thing to alarm the officials to perform a more thorough investigation, which turns up the actually incriminating evidence. They're not strictly speaking convicted by contradiction, but when their entire plan depended on not having anyone find out what they're up to, getting attention cast on them because of that contradiction is just as bad.
One of the Al-Quaeda bombers who attacked the US Embassy in Nairobi was rumbled this way. He was supposed to have committed suicide after his task (to throw a sound grenade into the courtyard to draw people to the windows before the bomb hit) was complete, but suddenly found a very good reason not to, and fled to a hotel in the suburbs. When the Agency interviewed him, he told them that he was wearing the same clothes he had worn on the day of the explosion. But they were pristine, whilst the CIA agents' clothes were worn after only a few days in the country. Then, he claimed he washed them. Not impossible. However, his belt, which he claimed to have been wearing on the day of the blast, was pristine, as opposed to the worn straps Kenya had made of the CIA's. And you don't wash a belt, so it must have been put on later, so the man must have been lying. When this error was pointed out to him, he spilled all.
Shibboleth: a word or custom specific to a particular group or subculture that most outsiders incorrectly identify or pronounce. Getting the name or tense of a local slang, street or landmark can identify someone as a foreigner at best (see the myriad differences in the ways Americans vs. Canadians pronounce words like about) and a German spy at worst (see the Isaac Asimov short story with the Star Spangled Banner). Shibboleths were used in history during ethnic and cultural conflicts as tests to distinguish an outsider trying to conceal themselves and the penalty was typically execution on the spot, as in the Word Origin, the biblical story in the Book of Judges of the execution of Ephraimite refugees who mispronounced "Shibboleth" as "Sibboleth". That Other Wiki has a full breakdown of the subtle differences in American and British English that are possible Shibboleths in everyday conversation.
A public defender recalled a story on The Moth Radio Hour, in which he was defending a man accused of smashing a window with a paint can by throwing it in from outside. It was an incredibly minor charge, and the prosecutor was willing to drop it if the defendant would just pay for the cost of replacing the window. However, the defendant swore up and down that he hadn't smashed the window (for extra salience, there was apparently a woman involved, that both the defendant and the window's owner were...having relations with), and wanted to go to trial. During pre-trial prep, the public defender noticed that the prosecutor wasn't going to call the police officer that responded to the original complaint, which struck him as odd. He, however, had spoken to the police officer, and he therefore knew that he was going to win the case. He called the officer to the stand (which is extremely rare, for a cop to be called as a witness for the defense), and asked if the owner of the window had allowed the officer into the room with the smashed window. Well, no, replied the officer. Alright, did you get to see the paint can? Well, no, replied the officer. Did you get to see the shattered window? Yes, the officer replied, but only from outside. And where was the broken glass? Well, replied the officer, it was on the outside of the window...