The usual response to a perp Saying Too Much. The perp, while maintaining his innocence, reveals information he could not possibly have known if he were innocent, usually the specific details of a murder. It can take the form of a Suspiciously Specific Denial. For full dramatic effect, the interrogator does not immediately point out this discrepancy, but continues the interview, often saving the kicker to the very end, as a sort of And Another Thing... epilogue. Even more dramatically, the interrogator may insist it wasn't poison and then probe the perp's reaction to this lie.
This trope must be handled carefully; when sloppily done it's likely to turn what should be a dramatic moment into a Fridge Logic. The most common mistake is making the piece of information something that the person who makes the "slip" could reasonably have found out without committing the offense. The second most common mistake is making the "slip" an assumption that could reasonably be made even by an innocent person.
One of The Oldest Tricks In The Book, and very much something the police use all the time in real life. Real police detectives usually hold back specific details of a crime and/or crime scene when making public statements. This has the dual benefits of possibly identifying a suspect and helping separate valid witnesses from useless leads. (Knowing these details may not automatically make someone the guilty party, but it's a big clue that they were at least present for the crime.) This is one of the reasons civil rights advocates warn people never to talk to the police without an attorney present. Even an innocent person can make assumptions about a case, and look guilty if they turn out to be right. For example, you might say, "I don't even own a gun," when you were never told the victim had been shot. It's even possible for the police to forget (or "forget") while testifying that they actually did give you the information before the interview began. Then you're screwed.
This trope can be invoked in works during a character's confession. Innocent characters attempting to take the fall for a crime they did not commit will probably guess facts about the crime that may not be true. If the facts are incorrect, they will be most likely be called out on it immediately or in a And Another Thing... manner. If the character is guilty, they could willingly give information only the perpetrator would know. This could be played to induce Squick.
See also: Conviction by Contradiction, Bluffing the Murderer, and I Never Told You My Name.
Happens all the time in Case Closed aka Detective Conan. Things like, "I have an alibi for 8 to 9 pm!" "How did you know when the victim died?"
Fushigi Yuugi has this during the Kodoku arc. Tamahome meets Miaka in the place they were supposed to before Nakago placed him under his control. He tells her, quite convincingly, that he only played along with Nakago's plans... at which point he asks her where Tasuki and Chichiri were, in spite of the fact that Miaka never told him Tasuki, whom he didn't even know at that point, would be coming along.
Sei Arisaka does this in Himechan No Ribon by saying that he knew who Pokota was even though Hime-chan had never told him, which is how she realised there was something more to him than original thought.
Liar Game used this too. The fact that Yuji knew that the stolen money was in the form of a check rather than cash told Akiyama that "she" was Mr. X.
Monster has this happen once too. In Episode Six, a couple of detectives are apparently transporting Tenma and Anna Liebert to their police station.(They actually work for Johan Leibert.) Tenma eventually figures this out when one of them calls him "Dr. Tenma" even though he only told them his name and not that he was a doctor.
Near the end of the Patlabor Manga, three detectives are interrogating the CEO of a company they're almost certain is the maker of the Griffon (which is still known to the general public as "the Black Labor").
Detective #1: So, you say you have nothing to do with the Black Labor? CEO: How many times do I have to tell you? I don't have anything to do with the Griffon! Or do you want me to just admit my "guilt"? Detective #1: If you did that in the first place, it would have saved us a lot of time. (Turns around) Did you hear that? Detective #2: Yup. Detective #3: Sure did. CEO: What...? Detective #1: Sir... How did you know the Black Labor is called "Griffon"?
Not quite the same, but related: In the third season of Sailor Moon, Mistress 9 is posing as Hotaru to talk to Sailor Moon. Eventually, she refers to Sailor Moon by her real name, which tips her off: "Hotaru...how did you know I'm Usagi Tsukino?"
Kurosagi Corpse Delivery Service uses this one when they find a corpse of a girl that turns out to be parts of seven different girls professionally embalmed and sewed together. Sasaki and Makino decide to go consult a guy who also studied embalming in America. They find he is running a beauty parlor, and he says he doesn't know anything about the body in the photo the girls show him. He offers them a free session when they get tired of chasing serial killers. Sasaki thanks him for his time and leaves. Makino protests that they didn't find anything out about the killer, and Sasaki answers it was the guy they just talked to, as they never said anything about serial killers, and there was only one body in the photo.
In Loups=Garous, Ayumi figures out Kunugi is an enemy when she asks him what time it is and his response is to pull out his monitor, indicating that he knows she doesn't have her monitor with her.
Armin in Attack on Titan makes good use of this. When trying to bluff the Female Titan, he uses specific wording like "the suicidal bastard" and "my best friend". Based on subsequent results, he correctly deduced that the Female Titan is actually one of his classmates since he was referring to Eren, since those names were the 104th trainee class's nickname for Eren and only people who know Eren and Armin personally would recognize it.
In Yu-Gi-Oh!, Bandit Keith accuses Joey of using someone else's entry card to qualify for the semi-finals of Pegasus' tournament, in a bid to get Joey disqualified. Joey freely admits that he was given his current entry card by Mai Valentine after losing his original one... but Keith had no reason to know that, unless he was trying to sabotage the other competitors' progress through the tournament by stealing their entry cards. Pegasus, who already knows that Keith was cheating during his duel against Joey, has Keith ejected from the tournament instead.
Used in Identity Crisis, when Jean Loring mentions the note at Jack Drake's crime scene to Ray Palmer, despite Batman removing the note from the scene before the press found out. Oops.
In Get Fuzzy, Rob asks who took his package. Bucky says he never saw that sweater, leading Rob to ask "How did you know it was a sweater?" Grounding ensues
In Transmetropolitan, our heroic journalist accuses the presidential candidate of killing his aide, to which the response is along the lines of "Of course we wouldn't kill her, she was a friend and a vital part of the campaign". See there how they admit that murdering some people would be okay in their book.
Later, The Smiler's campaign manager refers to the assassin as "he". Spider asks how he can be sure the killer was a man if he or she was disintegrated immediately after taking the shot.
In Hellboy: Conqueror Worm, local guide Laura Karnstein is leading Hellboy and Roger to an abandoned castle. While making conversation, Laura casually mentions that she read Hellboy's file and was impressed by his past exploits. As they reach the castle, Laura goes on ahead, but Hellboy stops Roger to warn him that Laura couldn't have read his file. Sure enough, Laura is not who she claims to be.
Turnabout Storm: The victim's identity is kept secret, no one who's not involved in the investigation or wasn't present in the courtroom should know anything about who he is. Cue characters that know too much info: Cruise Control, who knew the victim's identity; and Gilda, who knew he was a pegasus despite having no chance of directly seeing him according to her testimony.
Then there's Sonata, who refers to the broken and burnt Pinkie Iron Mk. V as a golf club, when it had only been referred to as a stick since her arrival.
Turnabout Substitution: Rhea makes this mistake twice during the final trial. She is able to handwave it with a hypothetical the first time around, but the second mistake ends up being her downfall. Apollo himself notes that Rhea would have gotten away with everything if she had just paid a tad more attention to what she was saying.
In Pokeumans Mindy gives herself away by accusing Brandon of stealing the Gemstone Files - documents that no-one in the base except the headmistress know even exist.
In The Stalking Zuko Series has a non-mystery related example. Katara eavesdrops on a conversation between Zuko and Aang about love. Zuko then asks her if Aang is also asking her personal questions, prompting Katara to say no, but also muse that Zuko must be the only one Aang's asking about love. Zuko then realizes that he didn't specify what he and Aang talked about. She manages to deflect suspicion before Zuko fully catches on that she eavesdropped on him, though.
Ed Exley from L.A. Confidential likes doing a variant of this in his interrogations. In particular, he tends to say something about them being guilty as if it were a fact, and note that the person never protests or reacts as an innocent person would. For example, in his first interrogation he tells the perp "It's a shame you didn't pull this a few years ago when you were a minor, you being an adult makes it a gas chamber offense." Later, after he's done and is leaving the room, he stops to say, "You know Ray, I'm here talking about you getting the gas chamber, and you never asked me what this is about. You've got a big guilty sign on your forehead." The kicker though is that the guys he's interrogating are guilty but not of the crime he's investigating.
"Vincennes mentioned a suspect he was hunting down. Rollo Tomasi?"
Minority Report has the villain realize the protagonists are onto him when he's caught in one of these. Anderton's wife asks about Anne Lively's death, and Burgess pretends not to know about it, but says he'll see if "anyone drowned a woman by the name of - what did you say her name was?". "Anne Lively...but I never said she drowned."
In Alone with Her, the tip off that the protagonist has planted surveillance cameras in the house of the girl he's courting is when she rejects him and he starts ranting: "...I did everything for you, but you want to go back? To what? Huh? To being alone? To this empty room? To that brush?" Earlier in the movie, he'd caught a live feed of her masturbating with the hairbrush.
In the Harry Potter and the Chamber of Secrets movie, Dobby the house-elf repeatedly does this, accidentally admitting to having intercepted letters from Harry's friends, sealing the entrance to Platform 9 and 3/4, and bewitching a Bludger to attack Harry, although the last two may have been intentional. Unlike the example above, these were also in the book.
In the Harry Potter and the Goblet of Fire movie, Barty Crouch blows his cover as Mad-Eye Moody by mentioning the graveyard Harry was sent to before Harry does. It's rather likely he didn't care at that point, though.
In The Departed, Billy Costigan, an undercover cop within the Irish Mob, narrowly escapes being ambushed by the rest of the gang during a meeting with his police superior and pretends to have arrived late after they have killed the superior. Another member of the gang, who is about to die and turns out to be an undercover cop himself, privately tells Costigan that even though he accidentally gave the wrong address for where the informant was going to be, Costigan was at the right one.
Used lightly in 1408 when Mike Enslin calls a hotel for a reservation in the eponymous room, which the staff says is unavailable, despite not knowing when he'll be visiting, since they don't want anybody staying in the room ever.
Averted in Sleuth; Wyke mocks Inspector Doppler for trying this tactic on him.
"Damn it. I always do things like that. You never said her name, did you?"
Subverted in the murder mystery Knight Moves wherein the protagonist knows the latest word in the serial killer's message without being told directly, because the killer namedropped a chess master and the word is that master's watchword.
Although the protagonist never realizes it and the film never makes a point of it later on, early in Red Eye Jack ends up letting slip the name of the protagonist's father, which at that point she had never told him.
Played straight so often in The Woman In The Window that it stops being suspenseful and becomes hilarious; the guilt-ridden professor lets slip every possible detail, including knowing the man was murdered (when the body hadn't turned up yet), knowing where the body was placed, that it happened at night, etc. His friends are so dense that they wave off every comment and never suspect him, but you would think he'd just learn to keep his mouth shut, especially when having casual conversations with the district attorney.
In The Count of Monte Cristo, Mercedes realizes that the mysterious Count really is Edmond when he tells her that "Edmond Dantes is dead." She had told him that her lover Edmond was dead, but not his last name.
A version of this is in the movie Patriot Games, after Jack Ryan's IRA informant gives him pictures of the people who had attempted to kill Ryan (and in a separate attack, his wife and daughter). Jack's superior dismisses the information, believing that mole is trying to mislead Jack. "All he has to do is show you a few pictures of a girl..." Jack realizes he never told the man he was looking for a female assassin and realizes the information must be legitimate.
In Wild Child, when Poppy is before the Honour Court for setting fire to the school, head girl Harriet accidentally reveals that she was actually the one who started the fire by talking about the very specific lighter that Poppy supposedly used, when no one has mentioned anything about a lighter.
Riggs: Hey, I didn't say his name was 'Jack' - You'd better start telling me more than Jack Shit.
In Scream 4, Jill turns herself in when she comments about having a similar wound to Gale, a fact only the one who attacked her could know.
In The Godfather Part II, Michael realizes that Fredo betrayed him when they were in a sleazy Cuban nightclub, and Fredo says "Watch this part of the act, it's really something", even though earlier Fredo had told Michael that he had never been to Cuba before. Fredo also mentions how "old man Roth" would "never come here", but that Johnny Ola showed him the place, despite an earlier claim of never having met either Roth or Ola. Actually kind of a double Inversion since Michael never tries to trip him up, but not being very bright, Fredo just blurts it out. The look of betrayal on Michael's face is classic and a definite example of Foreshadowing.
In Basic, this is subverted when John Travolta's character is chatting with Styles about the death of Kendal. Styles points out that the victim was coughing up blood and that poison is a reasonable guess.
Averted in Highlander. Lieutenant Moran, the lead detective investigating the beheading of Iman Fasil, tries to get Connor MacLeod to implicate himself using this sort of technique twice in the same conversation, but it doesn't work either time.
Moran: "Okay. What's that?" (indicates the plastic-wrapped Toledo Salamanca on his desk)
Connor MacLeod: (who knows exactly what it is) "A sword?"
Moran: "It's a Toledo-Salamanca broadsword worth about a million bucks."
Moran: "So you want to hear a theory? You went down that garage to buy this sword from that guy — what's his name?"
MacLeod: (who also knows who Iman Fasil was) "I don't know. You tell me."
Played with in the film, Primal Fear. Aaron is a suspect charged with murdering a Catholic Cardinal. The played with part comes in when Aaron claims to have spit personality disorder and doesn't remember what his other personality, named Roy, does. It helps him beat the first degree murder charges for an insanity verdict. During the trial, Aaron turns into Roy and he attacks the prosecutor while he's on the stand. This is causes a mistrial and the judge to find him insane. After the trail, arrogant defense attorney Martin Vail, who begins to feel sorry and care for Aaron, feels proud of himself, only for Aaron to intentionally let a detail slip that only Roy would know: Roy attacking the prosecutor. It's at this point that Aaron confesses that he never had split personality disorder and faked his Aaron personality to con everybody.
In Reindeer Games, when everything's seemingly over and Rudy, Ashley and Gabe - the survivors of the casino robbery - have gathered, Ashley mentions Rudy's cellmate Nick was stabbed with a shiv... but Rudy only told her his cellmate was killed; he never told her how. A few moments later, a now-doubting Gabe gets offed by Ashley, and Nick turns out to have been hiding...
In the film Cheetah, a brother and sister visiting their parents in Kenya adopt an orphaned cheetah cub whom they call Duma. When they have to return to the U.S., they plan to train her to hunt and release her back into the wild, but she disappears the night before they were going to leave. As their parents are driving them to the airport the next morning, they stop at the local general store where the owner says that it must be a sad day for the kids: leaving Kenya, losing their pet....The brother immediately jumps on this, asking why he thinks Duma is "lost." The store owner insists that by "lose," all he means is "releasing back into the wild where you will probably never see her again," but the brother is convinced that the owner wouldn't have used the word "lose" unless he knew about Duma's disappearance, and the only way he could know about the disappearance is if he was involved. The brother is right.
In Olympus Has Fallen, Mike Banning is a Secret Service agent who is apparently the only free survivor of an attack on the White House by Korean terrorists. He then comes across another survivor and fellow Secret Service agent who claims to have been hiding during the whole attack, but during their conversation mentions "This Kang guy is insane" referring to the leader of the attack. Banning then realizes that there's no way he could've known Kang's name if he was indeed hiding out in the White House the whole time and correctly deduces that he is a traitor working with the terrorists.
Played with in the film adaptation of The Da Vinci Code. In an early scene, when Fache still suspects Langdon of murdering Jacques Sauniere (but hasn't yet told Langdon that he's a suspect), Langdon's extensive knowledge of art gets him into trouble when he says that Sauniere was murdered in the Louvre's Grand Gallery before Fache actually tells him where the body was found. Langdon actually knew because he recognized the Grand Gallery's distinctive parquet floor in a crime scene photo, but Fache has a hard time buying that excuse.
The Radix: Hunting for Wurm, an escaped asylum patient, Adriana Borjia interrogates Cori. After Cori says "I didn't see him", Adrianna smiles and says: "I never said the patient was a man".
This happens in Encyclopedia Brown books quite a bit. Not generally for murders, but it happens.
One story had Encyclopedia figuring out which member of a gang robbed a grocery store, his only piece of evidence being a knife left stuck into a watermelon. When confronting the gang, one of the members says his knife is an inch longer... despite the knife never having been taken out of the melon, and the watermelon specifically having been described as "huge" so that even the longer knife blade would still be completely hidden.
Though, depending on the knife, this could be a reasonable deduction. If the knife opens out, it is probably just a little shorter than the handle. So, if you know you have a 5" blade, and you can tell the handle sticking out of the watermelon is only 4" long, you could make that assertion.
Another Encyclopedia Brown story has someone getting shot in the foot by a BB gun. One of Bugs' friends shows up, and Encyclopedia tells him to run to the kid's house and get his shoe. The kid grabs the correct shoe, and Encyclopedia points out that unless he was the one who shot him, he couldn't have known which shoe to get.
In at least one edition, it's mentioned he would more likely have just grabbed both shoes, which would probably have been sitting right next to each other—but the suspect specifically brought back only the one shoe. Still a case of Conviction by Contradiction, but not as bad as it could be.
Couldn't he just have seen which one had a hole in it?
Another story had a pair of rollerskates stolen from Encyclopedia while the latter was at the dentist. He asks the main suspect (a kid who had a doctor's appointment in the same building) if he was in Dr Vivian Wilson's office. The kid claims "I never heard of him until you mentioned his name" and that he didn't go near Wilson's office because he "had a sprained wrist, not a toothache" meaning that not only did he know that Dr. Wilson is a dentist but that he is a man despite his first name being "Vivian".
Also common in Two Minute Mysteries, by the same author - things like "Dr. Smith was murdered, where were you at the time?" "I haven't been to a dentist in years."
Colonel Graff does a slip up on the phone to Bean's caretaker (a very intelligent nun) when he says the name Bean told him about Achilles (pronounced uh-kill-eez). The nun points out that since Bean is from the French section of Rotterdam he would have pronounced it ah-sheel and correctly calls him out for spying on Bean's journal.
This happens in the third Brother Cadfael book, Monk's Hood. The prime suspect (the victim's stepson) thinks the murder was a stabbing, when it was actually a poisoning.
In a short mystery story called "True Lies," starring Lieutenant Johnson and Sgt. Bolton, the genius detective sergeant has narrowed down the possible murderers to two, but doesn't know which one. Since he thinks his lieutenant partner (who is the Narrator, and who would be Too Dumb to Live if he didn't know how to hide it from his fellow cops) is the genius detective, and so is dependent on him for his own genius, he asks the lieutenant for the solution. Our narrator doesn't know and is eating dry granola, so he chokes and says (as an excuse) "Tense!" This gives the sergeant the solution; the murderer was the one who referred to the victim in the past tense before it was generally known that she was dead.
Timothy Zahn's last book of The Thrawn Trilogy, The Last Command, features Niles Ferrier attempting to accuse Talon Karrde of hiring an imperial assault team to attack a group of smugglers as an example of the threat the Empire posed. He slips up when he mentions the name of the lieutenant leading the assault team before it's brought up by the person reading the planted evidence. He nearly slipped up before that by mentioning that incriminating evidence was on the datacard before anyone announced it had been found, only for Ellor to immediately confirm it had been found.
In Jo Walton's novel Farthing, the murder victim appears to have been stabbed. The police forensic techs figure out that he actually died of carbon monoxide poisoning, but don't reveal this to the press. A bit later, one character reveals that they know that the victim was gassed.
In Guards! Guards!!, Lupine Wonse's immediate response to Vimes reporting the destruction of the Elucidated Brethren's headquarters was a suspiciously specific "Any of them get out?" Because Vimes was distracted, he doesn't pick up on this until a Eureka Moment later on.
Inverted in Feet of Clay when Carrot becomes sure that Dorfl didn't kill Dr. Hopkins when he agrees to Carrot's statement that Dorfl beat him to death with an iron bar, when in fact he was killed with a loaf of dwarf bread.
Played with in Night Watch. After an antagonist officer tells Vimes of a break-in, Vimes asked what had been stolen. The other officer tries to invoke this trope, replying "Did I say they stole anything, sir?" and Vimes shuts him down with "Well, no, you didn't. That was me jumping to what we call a conclusion. Did they steal anything, then, or did they break in to deliver a box of chocolates and a small complimentary basket of fruit?" (Although to be fair to the officer, Discworld is home to anti-crimes such as 'breaking and decorating'.)
Vimes uses it once again in Thud! when talking to the Troll crime boss Chrysoprase. Chryosprase lets slip that his knowledge of a crime scene is greater than what the public would know. When Vimes calls him out, Chrysoprase dismisses the accusation as gossip that he heard from the Dwarfs. Or well, had Dwarfs beaten up or threatened until they told him. He did in fact have no connection to it.
Used in a sort of meta way in Making Money. Moist is being interrogated by Carrot, all while under the guise of being an upstanding pillar of the community businessman. When he tries to shut Carrot down due to him, Moist, being aware of this trope...
In Graham McNeill's Warhammer 40,000Horus Heresy novel False Gods, Loken knows that Erebus is lying to him because he pointed out that the interex had accused them of stealing a kinebrach's sword — and in fact, the interex had only accused them of stealing a weapon.
Inverted in A Widow for a Year when the policeman deliberately gives the press false information about a murdered prostitute, saying she was killed WITH a struggle when there was no struggle. This enabled him to dismiss the two men who confessed as they were covered in bruises and scratches.
Used near the beginning of The Haunting of Alaizabel Cray- the hero finds a young woman in the part of London infested by gribbly things, and asks the governor of a local mental asylum if he's lost any patients- he mentions her being found in the Old Quarter, despite not being told. In this case, it could be a reasonable assumption but the hero decides to be careful and gives a false description- a good idea, since said governor is part of the cult that had captured the girl...
This is how George Smiley discovers The Mole in the Secret Intelligence Service in John le Carré's Tinker, Tailor, Soldier, Spy: the man in question turned up at the Circus with not enough information about the unfolding Operation Testify crisis for him to have got it from the radio report, but too much to have overheard it from a phone conversation.
In the Thursday Next book First Among Sequels, Thursday and Spike accuse a plumber of stealing money from a pensioner. His boss joins in with the accusation, saying "A thousand pounds, from a defenceless pensioner? How could you?" Thursday and Spike had never mentioned the amount.
Reversed in Tom Clancy's Clear and Present Danger, when the FBI is investigating the mistreatment of prisoners on a Coast Guard ship. He says that one of the prisoners was executed (he wasn't, but they staged an execution by hanging to get a second prisoner to confess everything) to which the captain replies "We captured two prisoners, we gave you two prisoners alive, so who did we shoot?"
In one of the Fire Thief trilogy, the Avenger almost pulls this off and discovers the boy he is talking to is helping Prometheus when the boy mentions the shopkeeper looking for a spade (to dig up some buried treasure). But the boy quickly says he was running down the street shouting "half a million dollars for a spade."
A Nancy Drew book had a Jerkass character being poisoned, but ultimately recovering. A few days later, his ex-girlfriend taunts him about it as he tries to eat breakfast, stating, "You know, poison doesn't have to be a powder. Something could have been injected into that orange..." The only way she could have know what type of poison was used was if she was the assailant. Just change "doesn't have to be" to "wasn't" and you've got an admission of guilt that still wouldn't stand in trial.
On another occasion, someone asks what the "???" on their business card means. This is a Once an Episode thing which wouldn't normally be significant, but one of the group notices that they didn't actually read the card, and must have seen it before.
Used in one children's mystery, in which an unknown student was sending anonymous letters to the teacher, telling her all of the mean-spirited things said behind her back. This causes the teacher to be miserable and make all of the students feel horribly guilty. The only clues are that the mysterious student spells "sincerely" incorrectly and leaves a glob of ink as a signature. Eventually, they narrow it down to one person and trap her by innocently bringing up the ink blob. She blurts out "That's not an ink splotch, it's the shadow -". Busted.
In Katherine Kurtz's The Quest for Saint Camber, a member of the secretive Camberian Council is found dead in a secret passageway of the king's palace. In a conversation with Nigel (King Kelson's uncle/regent/heir presumptive), his eldest son Conall says the victim's entire name, which the younger man is not supposed to know. Nigel realizes Conall had been secretly working with the dead man (to obtain arcane powers reserved for the monarch) and killed him in that stairwell; Conall attacks his father with those powers and leaves him in a coma.
At least one of Tom Savage's stories (specifically Scavenger) has the protagonist mention something he shouldn't have known. This leads to a Tomato in the Mirror scene with a literal mirror.
Actually, there's some questionable writing here on Savage's part - the protagonist gives information that could easily be explained away, while the antagonist is the one who gives far too much information to authorities - yet the book acts like the protagonist has said something absolutely incriminating.
A case of the villain inadvertently using this against the protagonist occurs in Scorpia, when Julia Rothman tells Alex that Scorpia intends to activate a bioweapon that will kill a significant portion of the population. Alex, knowing that the weapon is designed to specifically target schoolchildren, blurts out that they can't murder children, causing Rothman to realise that Alex is a triple agent for MI6, and that MI6 have figured out how the weapon operates.
In the Father Brown short story "The Green Man", the victim is an Admiral who is found dead in a pond close to his home, on the evening when he was expected to return home from a longer sea voyage. Upon being told that the Admiral is drowned, the murderer asks: "Where was he found?" which tips off Father Brown. Note that Father Brown is older than radio. If the Admiral had drowned at any time during the voyage, his family would probably not have found out until his ship came back to England. Unless you know that he drowned in the pond, the reasonable thing would have been to assume that the body was lost at sea. Father Brown bites his tongue at the actual tip-off, but this trope comes into play in the big reveal at the end.
At the end of the A-to-Z Mysteries book The Lucky Lottery, the three main kids confront their prime suspect over a stolen lottery ticket.
Ruth Rose: And your fingerprints are on the mantel where you stole the Christmas card!
Dot Calm: You're crazy, kid. I was wearing glov...
In the Waco series by J.T. Edson, Waco uses this trick a few times to trip up a killer.
In Death in the Clouds, Hercule Poirot mentions to the main suspect that fingerprints were found in a bottle of poison used to kill the daughter of the first victim. The suspect says that is impossible, because he was wearing gloves.
In one of Agatha Christie's short stories, a man is killed by a blow on the head with a bronze statue. Two of the suspects—his wife and her lover—both confess to the crime: she says that she shot him, and he—that he stabbed him with a small dagger. On further interrogation, both tell that they assumed the other one was guilty and so lied to protect each other. But actually this trope is invoked: they are both guilty. They have planned the murder together and made the false confessions to make the police believe them to be innocent.
In Han Solo at Stars' End, Han finds that one of the three rebels he's transporting has murdered their leader, who just managed to scrawl the name of the destination planet, Mytus VII, in the table in front of him before he died. Han figures out who the traitor is by telling each one separately that he suspects another, and then telling them they're going to Mytus VIII, IX or X. He gets them all together, supposedly to research the target, and makes them show their datapads; the traitor is the one who mentally corrected it to the planet he already knew was the real destination.
In the various Law & Order shows, the detectives will often hold back certain details of the crime from the press, so they can test the veracity of any account from a suspect or witness. As many times as it's used to trip up the guilty, it will also expose someone attempting to confess falsely. For instance, a father taking the rap for his son's crime, not being able to describe at his allocution in court how and where he hit the victim.
Also Truth in Television not just for debunking people trying to protect the "real killer," but also, the higher profile a case, the more likely it is to have kooks falsely attempting to confess. Either because they're insane, they want attention, have avoided punishment for something else and want to atone out of guilt or they just enjoy fucking with the police.
Avoided in one episode when McCoy decides to go through with a generous plea deal with a suspect that covered "miscellaneous crimes" after the police told him the suspect's partner was dead. He exploited a loophole that allowed him to charge the defendant with crimes the DA didn't know about before making the plea; since the police never said the partner was murdered, he had no way of knowing his death was a crime.
He actually cuts the detectives off before they can tell him anything about the man's death, and then the issue becomes whether or not that was the obvious conclusion to draw.
Explicitly lampshaded in Law & Order: LA when the prosecutor asks the defendant, a Secret Service agent, if based on his long career and investigations that he'd agree that a suspect displaying knowledge of the crime was probably guilty. Defendant says yes. Prosecutor presents the text messages (sent from a smartphone they'd found concealed in the defendant's cell) to the victims' husband/father revealing information that only someone present in the house just before the attack would have known.
Subverted in an episode of Law & Order: Special Victims Unit. After a lengthy interrogation, Olivia catches a suspect mentioning a scarf that only the rapist would know about. The man confesses, is convicted and sent to jail. Eight years later it is revealed that the man is innocent. Olivia realizes that she must have mentioned the scarf early in the interrogation and forgotten about it. She essentially browbeat a tired and confused man into confessing to something he never did.
To clarify: he mentioned the color of the scarf (green), which was the hold-back detail. He has always claimed his innocence but Olivia refuses to believe him because he knew that detail, even when another crime is committed with an identical MO, and even as Amaro keeps trying to suggest that it's possible he was innocent. The turning point is when they re-interview the original victim and she casually mentions that the scarf was red, which leads to the discovery that the officer who logged the scarf as evidence made a mistake (he was red/green blind), and the suspect told her what the log said, not what actually was there, which throws everything about his conviction into question and allows the detectives to find the real doer.
Best use was probably "The Fox", where the killer, profiled as probably having OCD, has a minor Freak Out during questioning when he notices the pictures of his victims are out of order (which was done on purpose by the investigators).
The episode "A Real Rain":
Gideon: Is that why you stabbed him in the groin?
Suspect: It's what he deserved. note The victim had been stabbed in the head.
In yet another episode, their usual plan of withholding things from the media was thwarted by a leak and they had to find it quickly.
In one case of CSI: Crime Scene Investigation, Brass (after the fact) realizes that he should've been suspicious of the husband of a woman drowned in the bathtub from the beginning when he remembers that, while she is being carted away by the EMTs and it's not yet clear whether she is going to make it or not, the husband says: "I loved my wife." Whoops!
Subverted in Community in "Advanced Documentary Filmmaking". Chang, apparently suffering from "Changnesia" and calling himself Kevin, mentions Jeff being a lawyer. When Jeff points out that he shouldn't know this, seemingly catching him out, he recites a conversation Jeff and Shirley had earlier, wherein she mentioned him being a lawyer.
Chang: Jeff, thank you. When the Dean told me you were going to help me, I couldn't believe it. A cool, smart lawyer like yourself, reaching out to a little nobody like me.
Jeff (smirking): I never told you I was a lawyer.
Everyone exchanges concerned glances and looks at Chang suspiciously.
Chang: No, you didn't. Shirley said it, remember?
Happens on Monk. In one episode, the Captain shows a gun that had been used to murder the victim to the victim's friend. The friend points out the cracked handle on the gun and says that the victim was bludgeoned to death (which he was). Near the end, the Captain realizes that anybody who didn't know would assume that the victim had been shot, not beaten, and arrests him as he's about to kill Monk.
When an infant in foster care is found handling a kidnap victim's severed pinky in the park, Monk deduces at the very end that it was his foster parents, one of whom was told the child found a finger but replied back that he found a pinky.
The page quote comes from an episode where the killer points out that the police already had a suspect, calling him a "chain-snatching, dope-sniffing punk." Leland points out that the police hadn't revealed that the kid in question had stolen a chain to the public, thus only someone present when it happened could know about it. (On his way back from killing his wife, he broke his tail light. If he got pulled over for it, it would break his alibi, so he had to get it fixed. While he was there, he witnessed the kid robbing the auto shop and realized he was on camera, so he killed the shop clerk and took the camera footage.)
There was a hilarious subversion on the episode where Monk's medication interferes with his deductive talents. Monk attempts to nail the killer with "guilty knowledge":
Monk: How did you know she was wearing a bathrobe? No one said anything about a bathrobe!
One of the several clues that a midshipman's training sergeant had been guilty of his murder was that when Gibbs notified him of his (missing-presumed-deserted for several days) student's death, without mentioning that his death was murder, the sergeant's first question was 'Do you know who killed him'?
In a later episode, the suspect's wife assures Gibbs that her husband would never shoot a woman in the back. Of course, Gibbs hadn't mentioned to her or her husband how the victim had died.
Used in season 3 when a lieutenant working in the Cryptology unit was found murdered. Her boss asks Gibbs about her having shot herself, and Gibbs says later that only two people know how the Lieutenant died... one of her coworkers (who he'd interrogated) and her murderer. He then turns to the boss and asks, "How did you know she shot herself?'
An example from season 2: A woman with amnesia comments that "someone bashed that poor man's head in," when no one had told her how the man was killed. Unfortunately, by the time Kate realizes this, it's too late.
Played straight in the MacGyver episode "Hell Week," in which MacGyver catches a cheating contestant in a physics competition. The object of the competition is to create a barricade to a room with some unorthodox way to "unlock" the door. The good guy creates an optical illusion using a periscope to make the door look locked when it's really unlocked and vice versa. The villain eavesdrops on a conversation between his rival and a friend, and thus "wins" the competition...but he never actually looks into the room to see the periscope. Naturally, our hero notices this and...
Jeffrey (the cheater) :You all saw it. The door was opened; it was an optical illusion. He used that periscope.
MacGyver: That's right, he did. That's exactly what he did. But you had no way of knowing that. Jeffrey, you opened the door, but you never looked inside. You never saw a periscope - at least, not this afternoon.
Subverted on Homicide: Life on the Street: In the episode "Bad Medicine," Detective Lewis tells Villain with Good Publicity Luther Mahoney that a recently deceased thug obviously committed suicide. Mahoney scoffs, pointing out that the victim was shot in the back of the head and the gun was left on the table next to him. Lewis gleefully pounces, proclaiming that neither piece of information was released to the public and placing Mahoney under arrest. In the end, though, the state's attorney figures that there are any number of ways Mahoney could have learned it, too many to be beyond reasonable doubt.
Inverted in one episode. The detectives show one of the perps a bag with three guns saying that they found his fingerprints on one of them. The perp knows that they cleaned them, so asks the detectives which one it is. They point to another gun.
An example entirely between criminals: Brother Mouzone clues in to the fact that Stringer was responsible for Omar coming after him because Stringer seems to know that there was more than one assailant.
In an episode of Buffy the Vampire Slayer Willow realises that Malcolm, a person she is talking to on the internet, is not who they say they are after they reminded her that Buffy burned her old school down: information that Willow hadn't actually told Malcolm before.
Used frequently in Murder, She Wrote. In one episode, the suspect is asked to the police station and, while waiting outside the detective's office, is passed by the office security guard (not in uniform). He's then called in, where Jessica tells him her theory. His murder plan involved working late every night so the guard wouldn't know what he looked like, then re-entering the office building disguised as a delivery guy.
Suspect: Is that what this is about? You drag me here to see if the guard recognises me? Well, it didn't work! He didn't know me from Adam!
Jessica: What makes you think that man was the security guard?
One episode had Jessica Fletcher tell a group of suspects the murder weapon was found and the killer was identified because he later referred to it as a pizza cutter.
Happened in the Bones episode "Mayhem on a Cross".
A suspect in Without a Trace makes a pretty bad one of these. After only hearing a missing man's name and seeing a headshot of him, claims he'd "never hurt a guy in a wheelchair". Whoopsy.
In the episode "Bushwacked" an Alliance official tries to use this one on Mal, telling him they're looking for a brother and sister without mentioning the two are adults. Without batting an eye, Mal pretends to assume he's talking about children.
Harken: Alliance property, too. You could lose your ship, Captain. But that's a wrist slap compared to the penalty for harboring fugitives. A brother and sister. When I search this vessel, I won't find them, will I?
Mal: No children on this boat.
Harken: I didn't say "children." Siblings. Adult siblings.
Mal: I misunderstood.
In the episode "Trash", Mal meets an old friend Monty's new bride, an old enemy. They pull guns on each other and fight. After Monty separates them, Mal explains their mutual history to all present, and then:
"Bridget": You're a liar, Malcolm Reynolds!
Monty: ...now I ain't never got to tellin' ya his name.
Thereby proving, at the least, that she and Mal weren't strangers, as she had said. Had she not made that mistake, she still would have had to explain why their first reaction upon seeing each other was to pull a gun on each other.
Played for laughs in The Games- after taking an Albanian delegation sightseeing and setting fire to one of the members of the delegation's wigs, Gina confesses this to Bryan, who tells it to John... who tells it to a gossip columnist. Gina arrives at his house on the weekend and says she'll lynch Bryan for leaking the story, as she only told him, and John plays along before mentioning the name of the columnist. Gina immediately says 'I never said it was in Manny's column. How did you know it was Manny's column, John?' and he stammers until she gets up and walks out.
Used on This Is Wonderland. A white woman beats up a black man, thinking he was trying to rape her. He takes her to court, and she is so expecting the race card to get played that the following conversation ensues:
Crown Prosecutor Kaye: Or was it just because he looked like a rapist? Defendant: This has nothing to do with him being black! Crown Prosecutor Kaye: Black? I just said he looked like a rapist. You're the one who attached "black" to "rapist".
In "A Deadly State of Mind," Columbo finds a witness to a crime - a blind man. So they bring their suspect, Dr. Collier, in, and have a guy in shades walk in, sit down, and identify Dr. Collier as the man who nearly ran into him while driving away from the Donner house on the day of the murder. Dr. Collier claims to be able to use his medical training to tell the man is blind, and hands him a newspaper... which he reads perfectly. Columbo reveals it's actually the blind man's similar-looking brother, and there was no way Dr. Collier should've thought he was blind. Unless, of course, he had seen him while fleeing the scene of the crime.
In "Negative Reaction," Paul Galesko incriminates himself by grabbing the incriminating camera used to take pictures of his wife. The mistake is that he grabs the correct one right away, instead of mistakenly grabbing a different one.
In "Butterfly with Shades of Gray," there is a subversion, since Fielding Chase mentions that the victim was shot in the back. Most viewers assume that Chase only knows this because he is the shooter, but Chase does give a reasonable explanation to make it seem like he didn't commit the crime (since he made it seem like he was on the phone with the victim when he was killed) - by stating that the victim would have told him over the phone that someone was aiming a gun at him, but since he didn't, he obviously was turned away from the shooter.
A non-criminal example from The Cosby Show: Claire discovers her favorite mug has been damaged, poorly glued back together, and replaced. Heathcliff expresses his shock that one of the children would put it back in the cupboard. Claire never said it had been put back in the cupboard. Rather than quickly covering by stating that that's naturally where a mug would be, Cliff further steps in it by saying "way back in the cupboard"
Used in the episode "Red Badge" of The Mentalist. However, they already knew who the killer was—they were just getting him to confess.
Used in a last-second plot twist on Mathnet to uncover the leader of a gang of thieves who rob people's apartments after offering them a free weekend in the Poconos.
In the The X-Files episode "Small Potatoes", Mulder stops a seemingly innocent man in mid-speech, saying, "Hey wait a minute, wait a minute: how did you know my name was Agent Mulder?" The man runs.
Inverted in Human Target: Chance suspects the cops escorting his client of being the ones trying to kill her contact. They're too clever to let this slip, so he openly mentions an unknown fact about the meeting place (that it was on a bridge) and uses their lack of response to this "new" information to confirm his suspicions.
There was an episode of The Shield that used this trope very subtly. They mention to a suspect that the victims' clothing was found. When the suspect mentions the burned clothing, the interrogator doesn't react at all, and if you're not watching very closely you won't even know why she has a contented look on her face after the interview. Unlike most instances of this trope, the detectives don't gloat to the suspect or do anything else to let the audience in on what's going on.
In the Doctor Who serial The Keys of Marinus, Susan is kidnapped and her captor forces her to speak to Barbara over a futuristic alien phone. Later, the kidnapper accidentally lets it slip in conversation that she is aware they have spoken to Susan, even though it was not mentioned. This allows Barbara to realize her guilt.
Used again in The Time Meddler when the Meddling Monk (who is holding the Doctor prisoner) claims that he hasn't seen the Doctor but gives himself away by knowing what the Doctor looks like without Steven having told him.
In The Daleks' Master Plan, the Doctor realizes that Daxtar is a traitor because he knows that the Daleks' doomsday device requires a core of taranium even though the Doctor never mentioned it.
In "Marco Polo", Tegana mentions the location of a passageway in a cave he claims never to have visited.
In Supernatural episode The Man Who Would Be King, Bobby admitted to Castiel that he had suspected Cas of working with Crowley against The Winchesters. Hardly a breath later, Cas (who had just regained Bobby and Sam's trust) referenced an earlier conversation... that he heard while he was invisibly spying on the boys. Oops.
The League of Gentlemen, end of first episode in the Local Shop: just as a policeman investigating a missing person is about to leave the shop and go on his way, Tubbs blurts out "We didn't burn him!"
An episode of General Hospital had the cops interrogating a man found driving a missing woman's stolen car (He had carjacked her and left her on the side of the road, but had otherwise left her unharmed). The man tries to claim that he found the car abandoned and denies having ever seen the woman, but when the cops accuse him of foul play, he angrily declares, "I would never hurt a pregnant lady!" The cops had never told him that that the woman was pregnant.
In the Stargate SG-1 episode "Window of Opportunity", several planets, including Earth, are trapped in a Stable Time Loop, but only O'Neill and Teal'c are aware of what's happening. During one of the cycles, they arrive to the planet that has an Ancient device that causes the loop and meet an archaeologist O'Neill remembers from the first cycle. The man mentions Carter by name, causing O'Neill to notice that he didn't introduce her this time around, which means that the archaeologist is perfectly aware of the loop and is the one causing it.
Debra Morgan from Dexter realizes who really shot her and Lundy when the perpetrator asks her what it was like to watch the life go out of the eyes of the man she loved. This was far from common knowledge even in the station. She does consider that the person could have figured it out or been told by another cop, and investigates accordingly, but eventually concedes that there is no other explanation.
This is how Castle and Beckett identify Beckett's mother's killer in Castle. A man suspected of hiring the same contract killer is trying to cut a deal for full immunity from all charges, by insisting it's the only way she'll ever find the guy who killed her mother. Beckett later realizes that she never told the suspect which of her parents was murdered, and that he is the contract killer.
On another episode, Castle and Beckett interview the brother of a serial killer who had previously been convicted at a trial whose key witnesses are now being murdered one by one. He points out that he's been locked in an insane asylum since the trial, so who could have sent to kill the two witnesses? Castle points out they only mentioned one murder. (Turns out he totally didn't do it, he was just having someone follow the murders and try to stop the real killer, precisely because he knew he would look guilty.)
It is also how they catch the serial killer in the first episode. When they ask him where he was during his sister's murder, he immediately provides an alibi for all three murders. As Beckett points out, knowing where he was when his sister died is understandable, but the other two were strangers to him.
Killer: Al Mooney is insane! Nobody will believe what he says.
Lassiter: Hang on a minute! I don't believe anyone said the witness' name. You're under arrest.
An earlier example from Season 2, Episode 9 (Bounty Hunters) when Shawn and Gus identify the killer:
Juliet: Do you have an alibi?
Cole: I don't need an alibi, I'm not guilty.
Juliet: Oh, well, that's okay. 'Cause we can just look at the security cameras from the parking garage.
Cole: There were no cameras in that parking gara...
Season Six has Henry talking with his old partner after solving a case involving a couple of dirty cops from back in his days on the force:
Henry: I don't understand how they could do something like that. Partner: Well, fifty thousand dollars was a lot of money back then. (Cue Eureka Moment when Henry realizes that he never told the partner how much the other cops were being paid, and eventual season finale when Henry is shot for uncovering the secret.)
Home and Away had a guest character accidentally incriminate herself by identifying a fishing knife as a murder weapon. The police just called it a knife.
In an episode of Warehouse 13, an agent is discovered murdered under strange circumstances, and the team tracks down his old girlfriend to ask her some questions, during which she asks whether there have been any more electrocutions. Later, they realize nobody ever mentioned he was killed by electrocution. (Turns out she was also a Warehouse agent, who ran off when her boyfriend was killed during an investigation, and knows exactly what did it.)
In an episode of The Pretender, only the actual killer of a young girl knew what the victim looked like: There were no pictures in the news of the crime.
In the iCarly special iPsycho, Gibby, coming to rescue his friends from Nora, an Ax-CrazyFangirl who kidnapped them, he asks her if she's holding his friends here. She replies there's no one in her basement, confirming Gibby's hunch that they'd been kidnapped, as he then points out by saying that he never mentioned her basement.
Subverted in Terra Nova: after a false confession is revealed to be false despite knowing specific details of a crime, Shannon and Washington realize the actual guilty party made sure that the details were spread around to the colonists to cover any potential slip-ups he might make.
JAG: Played straight in "Washington Holiday", when the team were witnessing a failed assassination attempt on the Romanian royals. Told that the would-be assassin had named him as being behind the plot, the Evil Chancellor protested that it was ridiculous to accept the word of a woman who had been subjected to lengthy police questioning. Of course, nobody had mentioned that the assassin was female...
Minister Kepish: Your Majesty, how can you possibly believe the lies of a woman tortured by the Belgian police?
King Josip: How did you know the assassin was a woman, minister? They didn't even tell me that until an hour ago.
A literal interpretation of the trope occurs in the Alfred Hitchcock Presents episode "Road Hog": a salesman's refusal to let a family's pickup truck pass him - the youngest son has been injured in an oil rig accident and they're trying to get him to hospital - results in the truck going offroad into a ditch and their arriving too late to save him (had they gotten there in time he'd have made it), so they make him believe the oilrigger's wife has poisoned him and give him the same road hog treatment when he tries to get to hospital. He doesn't make it, and it turns out they'd simply given him aspirin - the stress of the situation gave him a heart attack.
In an episode of Covert Affairs, Annie is looking for a mole in a training academy, and realizes that one of the trainees was out buying illegitimate booze the night of a leak. She asked why that night, he said he knew he could sneak out because everyone would be busy dealing with another trainee who'd just been cut from the program. None of the other trainees knew she'd been cut until the next morning. (Circumstantial, except when she mentioned that, he attacked her.)
An episode of the new Hawaii Five-0 has the kidnapper of some college students ask for a woman who'd hid from them during the initial kidnapping, by name, be the one to deliver the money. When asked later how he knew she was in on it, Steve points out her name had never been published in the media to protect her identity.
On One Life to Live, a woman pretended to be a modeling scout in order to befriend a young co-ed and convince her to file a sexual harassment complaint against her professor (she wanted to get back at him for writing a tell-all book about her). When the scheme was discovered and everyone confronted the woman, she repeatedly and emphatically lied through her teeth about it and scornfully derided the girl's modeling aspirations—only no one had mentioned that this was how the two had met.
In the Sanctuary episode "Folding Man", the body of a Rebellious Rebel Abnormal named Aaron is found stuffed in a washing machine. When the group the man belonged to captures Zimmerman, Zimmerman asks them what they're going to do about "what happened to Aaron". The killer mentions the washing machine in his answer, and Zimmerman points out that the killer has no innocent explanation for knowing about the washing machine. The group turns on the killer.
Square One TV has an unusual variation where a guilty person is trying to frame an innocent, but then gets details of the innocent man wrong. In the Mathnet segment "The Trial of George Frankly", George confesses to the bank robbery, and says how sorry he is to his wife and children. The real George Frankly has no kids, proving that this George is an imposter; he was really a criminal George arrested years ago, who was trying to frame him for a bank robbery in revenge.
Another Mathnet example was "the Case of the Missing Air", involving a shock jock, Byle Dupe, suspected of robbing businesses who stopped sponsoring his radio show. While Dupe eventually is captured in the act, George Frankly and Kate Monday are convinced he's their man earlier on. Why? While questioning him on the robberies, Dupe claims to have been doing his radio show when the robberies took place - yet the time the robberies occurred were not made public.
In one episode of Flashpoint, when trying to find a kidnapped girl and her mother, the team goes to see the estranged grandmother who was visiting. She said she didn't know she even had a granddaughter and yet knew the granddaughter's name, alerting the team that she knew more than she claimed.
The Closer: Brenda's questioning of a suspect rattles him to the point of mentioning a detail of the murder he shouldn't have known in "A Family Affair".
A variation in Person of Interest had Carter interrogating several suspects to determine which was former military. All of them were, but were hiding it due to being mercenaries. During the interrogation, Carter demands to know one suspect's military service number, but uses an obscure term for it. When he angrily replies he never served in the military, she demands to know how he knew the term.
Jenna:(eerily calm throughout) Jenny McCarthy died? But who could have been slowly poisoning her? Was she poisoned? I have no way of knowing, because I'm just hearing about it.
The eponymous Frost pulls off a straight "but I never said it was murder" version. It fails as the suspect calmly points out the police don't send senior officers to inform people that their employee has been in an traffic accident.
In an episode of Becker, Dr Becker is accused of being racist after a journalist construes angry comments he made about people he knows and confronts the journalist on a radio station and clears himself by pointing out he was angry on those people not because of their race but the things they did which annoy him (eg. Disliking rap music being played in public because it's too loud, not liking his Asian taxi driver because he crashed his car before). But when the journalist talks about Becker's Puerto Rican neighbor, Becker asks how the journalist knew his neighbor's race when Becker never mentioned it. It is then when Becker figures out that the journalist was the real racist as he was using Becker's comments to hide his own racist stereotyping.
In a second season episode of White Collar, an old friend of Neal's landlady shows up, fresh out of prison, looking for another big score. Neal has to go undercover with the guy to try and take down the murderer running the scam. The old friend almost pooches it by letting slip a bit of info he shouldn't have. Good thing Neal can tap dance on air when things get sticky.
Agents of S.H.I.E.L.D.: In "Turn, Turn, Turn", Garrett accidentally outs himself as The Clairvoyant when, in an attempt to convince the team to kill the loyal agent they've mistaken as the Clairvoyant, he lists all of the Clairvoyant's crimes... including something Coulson learned from Raina that he never told anyone else, meaning there is no logical way that Garrett could know it. You can see the moment that he realizes what this means.
In Homeland, when Carrie and Brody are having a romantic getaway at her family's cabin, she tells him that unfortunately she doesn't have any of his favorite tea, Yorkshire Gold. Unfortunately for Carrie, that is, seeing as Brody never told her what his favorite tea was, and he realizes instantly that she must have been spying on him.
The Cranes of Ibycus is a classic example of this trope making it Older Than Feudalism. According to a legend first recorded in the 2nd century BCE, the ancient Greek poet Ibycus was murdered by bandits on his way to Isthmian Games. Only the Cranes flying above witnessed the murder. Later the criminals gave themselves away by pointing out 'The Cranes of Ibycus' to one another in public.
A "Five Minute Mystery" titled The Return of Mr. Lawrence plays it by the book: a murdered woman's maid accuses the woman's former husband of poisoning her. The police never said it was poison.
Pip Bin: The body was covered in hundreds of tiny stab-wounds? Inspector Whackwallop: Aha! I never said the body was covered in hundreds of tiny stab-wounds! Ripley: Actually, you did. Whackwallop: Did I? Damn, that normally works. Aha! I never said he was an apprentice carpenter! Pip Bin: And nor did I. Whackwallop: Damn.
In NPR's radio adaptation of Star Wars, Leia's rebel allies inform her of the Death Star's existence. Later, she's being told about the weapon by an Imperial officer, and accidentally slips the weapon's name even though the officer hadn't mentioned it. Things get ugly from there.
In David Mamet's Glengarry Glen Ross, Levene blows it by admitting he knew Williamson had already cashed Lingk's check, something no one but Williamson and the person who robbed the office would have known.
In the Touhou fangame Aya Shameimaru: Touhou Attorney, based on the Ace Attorney games, the very final choice you have in the last case in the game hinges on this. While it's easy to miss, a Genre Savvy player can easily pick up on the extra detail without even considering the situation. Specifically, outside the detectives and the attorneys, no one but the one who planted the evidence would know in which pocket it was found.
During the first big plot twist of Chrono Cross, Lynx had just switched bodies with Serge and was about to kill his old body with Serge in it. He told Kid that he was going to do it to avenge Lucca for her, but then Kid just realized: while she did tell Serge that Lynx had taken away Lucca from her, not once did she say her name! Of course, this revelation comes too late... Needless to say, it seemed like a bad choice of words for Lynx.
In Persona 4, Adachi reveals himself by saying that he thought everyone was sure that "Namatame put them in [the television]" — no one but the murderer and the protagonists could have known that that was how the victims were killed. He had also cast suspicion on himself in an earlier instance when the protagonists find a list of everyone that Namatame had put into the television: Adachi shows no surprise at the contents of the list despite the fact that it included people who were rescued before being murdered (and were therefore classed as mere "disappearances" that had no relation to the murders).
In Mass Effect 1, when Saren is facing accusations of attacking a human colony and killing another Spectre, Nihlus, he addresses Shepard as "the one who let the beacon get destroyed." Shepard can respond using this trope, saying the only way he could have known that is if he was there. However, Saren quickly rebuffs him/her, saying that Nihlus' files transferred to him upon his death.
In Indigo Prophecy, taking too long to answer Detective Tyler (or Detective Carla depending on previous choices) can lead Lucas to blurt out one of these leading to an instant arrest and game over. Specifically, Tyler or Carla is in the middle of asking Lucas where he was on a certain night, and if you take too long to answer, Lucas blurts out that he wasn't even at the restaraunt where a guy got murdered...then as Tyler or Carla points out, since they mentioned neither a restaraunt nor a murder, why would Lucas randomly assume they're asking him about that particular murder unless he had something to do with it?
In Professor Layton and the Diabolical Box, the fake "Flora" is revealed when he looks at a photograph of the Elysian Box and mentions the cute goat on it. The picture was missing a piece that identifies the emblem as a goat (it looks more like a frog without it), meaning "Flora" had seen the mysterious box before, making him the thief.
In Professor Layton and the Last Specter, a surprisingly spoiler-free AND murder-free version of this is when Layton and co. are looking for some medals with certain parts of a raven on them. One of the kids you confront says "We don't know anything about a medal with a raven's tail on it!" To which Layton replies "I never said anything about a tail."
In L.A. Noire, the DLC case "A Slip of the Tongue" features one of these. If Phelps and Bekowski manage to catch up to Jean Archer, they'll mention Belasco (another suspect, and Archer's accomplice). She later drops his full name "James Belasco", which confirms to Phelps that she's connected to the case.
A kidnapping suspect in Kara no Shoujo admits that he has some relation to the person witnessed actually taking the person away before the name of the person is revealed. Woops.
Used in one of the in-game skill books in The Elder Scrolls series (it levels up your Alchemy). The author of the book recounts a dinner party where everyone (including the author) is spying on the host. After the soup course is brought out, the host declares that all spies in his household have been poisoned, and the antidote is in the soup. Everyone tries to hold out, but one eventually gives in and frantically drinks the soup. It turns out that the soup contained the poison, and the host was testing his employees.
Baten Kaitos Origins uses the "innocent character taking the fall" variation. When Juwar is asked for more details of what he did in the city of Mintaka as the Mourning Mistral, he tells Sagi that he planted the bomb in a nearby building after the election speeches...not knowing that the real Mourning Mistral broke their pattern of targeting buildings to target an airpod instead.
In the video game of Batman Begins, Arkham Asylum doctor Emma Thomas (not in the film) has been suspicious of Dr Crane for a while. When Crane's thugs ask her why she was in the basement looking at the canisters, she claims she got lost and doesn't know anything about the toxin. The thug replies "I never said anything about a toxin."
In The Witcher Geralt finds an old diary potentially implicating a traitor to the kingdom; the author of the diary, Ostrit, is dead, but new notes were scrawled into the margins. Later, he meets a Count who, after hearing of the book, asks for "Ostrit's diary". Geralt quickly notes that, in the conversation, he never said that the diary was Ostrit's.
One example in the third game has the murderer give himself away by correcting the colour of a poison bottle after Phoenix does some Lying to the Perp.
Another example in the third game is in the second case, where the murderer reveals information he couldn't possibly have known unless he was at the scene of the crime when the murder had taken place. As, during the only other time he could have learned this information, which was during the trial, he himself was on trial in another courtroom for a different crime.
In the fourth game's third case, an apparent witness who's trying to convince the court that she didn't see the crime slips up and mentions that the victim was shot. The crime was put on a "gag order", so no one apart from those investigating it, or someone who saw the crime happen, should know those types of details. It actually turns out she was telling the truth when she said she didn't SEE the crime. She's secretly blind.
In the first case of Ace Attorney Investigations 2, De Killer refers to the victim by his full name during a cross-examination, while up until then Edgeworth had only ever refered to him by surname (and, in fact, didn't even know his first name until that point). It doesn't mean what you think it means, but it does reveal him as more connected to the case than he claims.
An example comes in case 2 of Investigations 2, in which Frank Sahwit comments that he swears he didn't hear the scream of the person who discovered the body. Edgeworth points out that, normally, if someone is told a scream rang out during a murder, that'd they'd assume it belonged to the victim, not a witness, and that he never mentioned who they believe the scream belonged to. Frank admits at this point that he was the one who found the body.
Sawhit does it again later in his testimony, where he mentions a ring on the victim's body. Since the body was positioned such that a sheet covered his hands, Frank couldn't have known it was there if he had only observed from outside the room, as he claims. It turns out he'd managed to enter the room and look at the body up close.
In the same case, during a chess logic, another witness refers to Edgeworth as "Prosecutor Edgeworth". Edgeworth's points out that he never one told them his profession leading Edgeworth to conclude that the witness was eavesdropping on his earlier conversations.
It also turns up often in Logic Chess segments. Chances are that, if you see a witness mention something you haven't heard of before, or that they couldn't possibly have known, you need to jump on it.
Souma Miou is outed as the one who had been bullying Rizu in A Profile because when confronted with a little evidence blurted out the location the evidence had been found in.
In Virtue's Last Reward, this is how Sigma gets Dio to reveal he was the one who planted the bombs in some of the routes. Sigma reveals, from information he gathered from time-jumps, that he knows about the Myrmidons, and about Brother. Dio insists he doesn't know anything about who the Myrmidons are, and he doesn't know anything about some old fart like Brother. Well, Sigma never actually mentioned the Myrmidons were people or that Brother, their leader, was an old man, so how would Dio know that...unless they sent him?
In Danganronpa, this is how you discover who the culprit of Chapter 2's murder is. It's none other than Mondo Oowada, the Super High-School Level Gang Leader. Another student, Celestia Lundenberg, recently told everyone that the murder victim, Chihiro Fujisaki, was wearing a jersey when Chihiro went to go exercise. When Kiyotaka Ishimaru asks about the jersey, Mondo Oowada pipes up, oh, so the victim was wearing a blue jersey then? His was black!...but Celes never told anyone but Naegi what color the jersey was, so how would Mondo know that unless he was the one that brained Chihiro over the head with a dumbbell?
In Chapter 3 Celestia herself is ironically nailed the same way: shortly after the discovery of Ishimaru's body she comments that the culprit is "going to kill the rest of us just like he killed the guys" despite having remained in the same floor with Yamada's body the whole time and thus had no way of knowing that two people were murdered.
Chapter 3's culprit of the sequel is also uncovered like this. Mikan spoke about the details of Ibuki's supposed "suicide video" when Hinata was the only one to have seen it.
Then in Chapter 4 of the original, Hagakure trips over this. He points out the message written in blood naming Fukawa as the killer... only, among other things, the magazine was hidden in the rack at the time the body was found, and Asahina had kicked him out of the crime scene before he could take more than a look, so how did he know about it?.
In Namir Deiter, Ferdinand is drinking away his sorrows after a run in with Joy. Isaac, Joy's most recent ex, talks to him when Blue tells him about Ferdinand and Joy. Isaac slips out Joy's name, and Ferdinand wonders how Isaac knows about Joy. Isaac tells him that he saw Ferdinand and Joy earlier, guessing that he was upset about her.
In one Shadow Unit episode, the gamma, whose manifestation involves causing real bullet wounds with a broken, unloaded gun, gives herself away by being the only person to have heard a gunshot at the death of her latest victim.
Chakona Space: Chapter 3 of Doove's Flight of the Phoenix series features a pair of "Ambassadors" who kill their servant and dump hir body at the base of a stairwell. Captain Yote announces the death of said servant (without including details) to them and one of them snarks about making sure the stairwells are properly safe, instantly implicating "him"self in said death.
Lawyer: Will you tell the court your whereabouts at the time of the carjacking?
Willie: I was alone in me Unabomber-style shack; I had nothing to do with that carjacking.
Lawyer: Carjacking?! Who said anything about a carjacking?
[galley and jury murmurs]
Willie: But, didn't you just say—?
Lawyer:I'll ask the questions here, Carjacker Willie!
Another instance in a Simpsons adaptation of Hamlet. Prince Hamlet (Bart) is trying to get his uncle Claudius (Moe) to confess that he killed King Hamlet (Homer):
Krusty as a jester: Now we would like to warn you, our performances tend to make audience members blurt out hidden secrets.
Moe/Claudius (nervous): Oh, boy...
Krusty: Okay, we're going to up open it up with a little improv. Somebody shout out a location.
Bart/Hamlet: This castle!
Krusty: Okay, how about an occupation?
Bart/Hamlet: Usurper of the throne!
Moe/Claudius:[tugs at his collar nervously]
Krusty: I think I heard usurper of the throne. Now, finally I need an object.
Bart/Hamlet: Ear poison!
Moe/Claudius (nervously to Gertrude/Marge): Do you have diarrhea? I have diarrhea... [tries to leave]
[Sideshow Mel, Krusty and the Monkey begin acting out a situation in which Mel starts pouring ear poison down Krusty's ear]
Moe/Claudius: Wait a minute, I didn’t use that much poison!
Moe/Claudius: I mean, I didn't use that much poi, son, at the royal luau. Hehheh.
Or, in the French Canadian dub:
Moe/Claudius: J'ai pas mis autant de poison!
Moe/Claudius: J'veux dire, j'aime le miso de poisson. C'est un plat japonais. (I like miso fish. It's a japanese meal.)
Beavis and Butt-Head went on trial for throwing eggs at Mr. Anderson's house. They were almost set to be pronounced not guilty when the plaintiff's lawyer noted that Butt-Head had called them "rotten eggs" instead of just "eggs." How did they know they were rotten? They could only stammer, and within a minute the jury pronounced them guilty. (Can you blame the jurors?)
Averted in Teen Titans: Trouble in Tokyo. A girl who works for the villain approaches Beast Boy and calls him "otaku." Beast Boy takes it to mean that she thinks he's cute, when it actually means "comic book geek", which is something only someone who had been watching him could have known about.
He was moping around outside a closed comic book factory. One would assume someone moping on the steps of DC or Marvel's printing plants would be declared a comic book geek too. Though it really doesn't matter, as Beast Boy couldn't understand it anyway.
Though he did say they should have gone inside the manga factory to begin with, only to be given a Dope Slap by Raven.
Fillmore!: Fillmore is discussing a case with an old friend who's one of the witnesses, and he mentions that 4000 counterfeit baseball cards are still missing. She tells him not to worry, because "it's not like four thousand Cal Ripken cards are gonna just disappear." Fillmore realizes that she must have the cards, because he never told her what player was on them.
Batman Beyond: Terry visits Willy Watt in Juvie hall, whom he suspects is the "ghost" terrorizing his high school with telekinetic pranks. During their conversation, Willy brings up the school incidents, even though he's had no visitors or callers since having been locked up (and presumably the incidents never made the news).
Star Wars: The Clone Wars: In the episode "The Hidden Enemy" one of the clones betrays his brothers. Captain Rex and Commander Cody discover a listening device planted in their command center, and begin to question a squad of suspected clones about it. The turncoat mentions the Jedi had left - something only Rex and Cody knew at the time. Though strangely enough, he wasn't one of the suspects.
Clone: No! Sir! I'm telling you, I did not- Slick: It's okay, you don't have to say anything till the Jedi come back and talk to you. ... Cody: What did you mean, "'til the Jedi come back?" How did you know the Jedi were gone? Slick: I really wish you hadn't noticed that, Sir...
Spoofed in the American Dad! episode "Black Mystery Month". A detective quizzes Steve at the scene of a murder and is instantly suspicious when Steve mentions details that are clearly visible at the scene.
Detective: I'm afraid the curator has been murdered. Steve: Oh my God, someone killed him?! Detective: Funny, I never said he was murdered. Steve: Yes... yes, you did. God, he's wedged into the mouth of a giant bust of George Washington Carver! Detective: That's classified, how do you know that? Steve: Uh, I can see it from here. (the detective takes half a minute confirming that the body is visible from where Steve is standing) Detective: Okay, that checks out.
In the Sally Bollywood episode "The Party", Sally and Doowee are investgating who gatecrashed a party. Whilst interrogating a known-gatecrasher, the gatecrasher points that it couldn't have been him and his buddies, since they don't wear masks when they gatecrash. It's then pointed out that no-one had mentioned that the gatecrashers were wearing masks, and a Chase Scene ensues.
One of the villains in Big Top Scooby-Doo! gives himself away by referring to the black diamond, despite supposedly having been kidnapped when the gang learned that carbonado referred to a black diamond.
It's possible to assume details about a crime without realizing that you're doing it, which can lead to self-incrimination even if you're innocent of the crime. This is one of the many reasons why you're not supposed to talk to police without a lawyer present.
This is the reason why newspaper reports about homicides tend to be deliberately vague. The police withhold crucial information until they have had a chance of interrogating the suspects in order to catch suspects in these situations and weed out false confessions.
Suspicion that Wallace Souza had ordered or co-ordinated Brazilian gangland murders for his TV show Canal Livre grew when he approached a still-smouldering body in a forest, saying “It smells like a barbecue,” he says. “It is a man. It has the smell of burning meat. The impression is that it was in the early hours... it was an execution”, even though the police had never given a time of death. Also, he tended to arrive a little too quickly at the scene of the crime. He died before he could be prosecuted.
As seen on the Saying Too Much page, where a woman was arrested as a suspect in the murder of a man that had won the jackpot and had disappeared, then turned up dead several days later. She was also under suspicion of embezzling it, and after being released from a round of questioning tearfully professed that she had been falsely accused of shooting another human being. Police had yet to release exactly how the man had died.
Macedonian crime reporter Vlado Taneski became a suspect of being the Serial Killer that stalked Taneski's own hometown and he often wrote about, when he included copious details about the crimes that had not been disclosed to the public, such as the type of phone cord used to strangle the victims, or the fact that it had also been used to tie them.
Judge Judy once handed down a judgement in less than thirty seconds because of this. The plaintiff was arguing that the two defendants had stolen her wallet, hence the trial. After the plaintiff was finished listing the items that were in the stolen wallet, one of the defendants piped up that there was no earpiece in the wallet...but he had to have stolen the wallet to know that.