The criminal is caught, comes up for a trial—and then it turns out that he wasn't read his Miranda Warning, or the Cowboy Cop forgot to get a search warrant, or the confession was obtained via Jack Bauer Interrogation Technique. The judge is forced to throw the case out and the (alleged) crook walks free to offend again while their victims are left to suffer the ruling of a legal system more concerned about "procedure" than "justice".
In stories where a Vigilante Man or Cowboy Cop is the protagonist, the the bleeding heart judiciary will accept any half-baked excuse for letting criminals go free. This is often a case of artistic license as in Real Life technicalities frequently don't apply the way they are depicted or may not even exist. If the accused person is the protagonist, then the "technicality" will actually be an albatross for them, because no one will believe they're actually innocent until the end of the story/series when the actual criminal is found.
Most prevalent back in the 1960s and 1970s with the vigilante justice fad in fiction, after several court decisions seemed to tip the balance of the legal system far in favor of the accused. Since then, Real Life police and other law enforcement personnel have had these changes included into their training to avoid screwing up their cases, and the fictional versions have become rarer. It still happens, but unlike in fiction, it's more often the excuse for the acquittal, rather than the reason (ie. a Judge or Jury doesn't feel the person is guilty in spite of the evidence, and exploits the technicality as a legal grounds to dismiss the case).
In a Police Procedural, such as Law & Order, this will usually come in at the first quarter-hour mark, when the initial case falls through, and the DA tells the cops to find some non-tainted evidence or charges to rebuild a case from.
The Amoral Attorney with Rule Fu Stronger Than Yours loves taking advantage of this.
Another episode involves an Amoral Attorney who gets his client off for killing his girlfriend in front of Togusa by spinning Togusa's actions (repeatedly shooting the man's cyborg arms with his sidearm) into Police Brutality and Fantastic Racism against cyborgs. Then, for an encore, he tries to release Togusa's involvement with Section 9 (a public secret) as part of the proceedings. This last part backfires on him: Although his client is released, Aragaki responds by having the attorney and the client killed in a car accident.
Bob Ingersoll's column on law as (mis)portrayed in comics, The Law Is A Ass, included several discussions of comic-book villains getting off on technicalities, and why it wouldn't actually have happened; this and this are good examples.
It has even been played, at times, that confinement to Arkham Asylum is less the result of an Insanity Defense on the part of villains, but a legal technicality directly resultant from the fact that they were arrested and investigated by Batman rather than an agent of the law, which presumably would make evidence inadmissible if the cases went before a jury. In reality, the opposite is true — any evidence collected by a private citizen is always admissible, without exception; the exclusionary rule only covers evidence collected by government action.
In Doom Patrol #90, the previously-captured Madame Rouge is on the loose again because "A crafty lawyer had her freed on a technicality!" Handwaved by not revealing what the technicality was—and Madame Rouge was promptly deported.
District Attorney Adrian Chase became The Vigilante, because he was tired of seeing "by the book" arrests being quashed on technicalities. As Bob Ingersoll pointed out, this strongly suggests he became a DA without actually knowing what "by the book" means.
In the Ultimate Spider-Man comics, being apprehended by the Web-Slinger (and possibly any costumed vigilante) is a violation of your civil rights and is the source of Joker Immunity for anyone he has a hand in bringing down, particularly the Shocker, who gets a "Get out of Jail Free" Card for breaking out of jail and his original crimes which Spidey had nothing to do with. As of Ultimatum, the DA's office has done absolutely nothing about this loophole, instead blaming Spider-Man for their cases getting tossed. The Punisher is listening when this is brought up at Ryker's— a rapist says that he's free as a bird, because Daredevil beat the crap out of him as he was about to nail a thirteen-year old in a house he broke into— and that's how the reader discovers that nesting the bowl of a spoon in your palm with the handle between your middle and ring fingers will enable you to slash open someone's throat.
The Kingpin was cleared of murder charges after his lawyer got the video of the murder ruled inadmissible. Even though news station played the video for all to see, the citizens of New York treat this as the same thing as him as being completely innocent.
Parker tries to bring it up during class, and the teacher gives him detention. The implication is that everybody knows he bought the cops off, and is therefore the de facto master of the city - and their lives are at risk if they bring it up.
Scorpio in Dirty Harry, who got off due to Harry Callahan illegally obtaining the evidence that would have convicted him and using the Jack Bauer Interrogation Technique to make him talk concerning where the girl Scorpio kidnapped was, since the DA said he "couldn't condone police torture." This would only invalidate the confession of that case (even without Scorpio's confession, there's more than enough hard evidence for a conviction), but certainly not Scorpio's attempted murder of Callahan, assault with a deadly weapon, possession of an illegal automatic weapon, and kidnapping him, which is enough for a life sentence by itself.
Scorpio was wearing a balaclava when he attacked Harry. Harry searched his room without a warrant (because he thought he was running out of time to save the girl) invalidating the weapons found there.
However, Scorpio had the same, fresh knife wound Harry (legally) inflicted on the man in the balaclava and had the same voice, and the search is legal under exigent circumstances - the girl was in imminent danger, and Scorpio was trying to escape, and Harry had probable cause to suspect Scorpio. In Real Life, that alone would be enough for a conviction (not to mention that they might not have believed anything Scorpio said anyway).
Exigent circumstances were first allowed in the California Supreme Court decision People v. Ramey in 1976, 5 years after this film was made, so it didn't apply then.
In the sequel, Magnum Force, the film opens with a known racketeer, his attorney, driver, and bodyguard being executed by a traffic cop after the former gets off on a technicality for the killing of a labor reformer and his family.
The Sally Field movie Eye For An Eye has this as its premise, as a woman who loses her daughter to a rapist tries to get him behind bars, but seeks her own kind of justice on him after he gets off on a technicality. The tagline of the movie is "What do you do when justice fails?" (become the star of Brothers and Sisters?) In Real Life, at the very least, the killer's constant making faces at Field would earn him a bunch of "contempt of court" charges.
Also, in the film the killer got off because the prosecution didn't disclose some evidence — before he got to trial! In Real Life, it would probably mean a reprimand, them getting ordered to reveal that...and going on to trial.
Re-examine. The evidence in question is a small amount of blood - enough for the prosecution to identify the killer with their own tests, but not enough for the defense to run tests of their own. The defense was invited to have their own experts participate in testing the blood - they declined. It wasn't until the trial that they sprung the technicality. They purposefully refused to participate in the investigation so their killer rapist (who already had a record of stalking) could go free. Please tell me I missed something.
If they had a chance to examine it themselves and this was disclosed, that probably wouldn't be a violation. As usual, it was contrived so the criminal gets off, giving the protagonist an excuse for vigilantism.
In the A Nightmare on Elm Street series, child-killer Freddy Krueger was let off because, as expanded on in Freddy's Dead: The Final Nightmare, a drunken judge failed to sign the search warrant in the right place, so the parents of Elm Street banded together and burned him alive. A case of Hollywood Law, as thesearticles from the column "The Law Is A Ass" details why that particular arrest was, in fact, valid and wouldn't have been tossed out.
The circumstances of Freddy's arrest are expanded on in a few books (including the Freddy vs. Jason novelization). Some Cowboy Cop suspicious of Freddy actually broke into the Krueger house and utterly trashed the place looking for him, stumbling across Freddy's hidden "trophy room" (where he kept scrapbooks containing newspaper clippings and such); afterward he rushed to the power plant, found Freddy there and brought him in.
The first episode of Freddy's Nightmares stated that Freddy got off simply because the arresting officer failed to read Freddy his Miranda rights (which is also not legitimate, since it only means any statements he made couldn't be used, but other evidence could be.
The film The Star Chamber is about a group of vigilante judges tired of crooks getting let off on technicalities.
Ironically, one of the two illegal searches highlighted in the movie (when police officers searched a trash can where a serial killer had stashed his gun) would actually have been legal because the suspect wouldn't have a "reasonable expectation of privacy" in its contents. The other search, in which they searched two suspects' van because the DMV incorrectly reported it as unregistered, became legal a year after the film's release when the Supreme Court codified the good-faith exception.
In the Al Pacino movie ...And Justice for All, this is cruelly inverted with Jeff, whom Kirkland can't get off although he's innocent because of a technicality.
In the thriller Someone to Watch Over Me, the villain is released after being arrested for murder because no one read him his rights, even though he was never interrogated and no statements made by him were used as evidence against him. Especially facepalm-worthy, since the movie actually (apparently unwittingly) provided a legitimate reason for why he might be released: he isn't represented by counsel during a lineup, even though he requests it, tainting the resulting identification (which is the prosecution's whole case).
In the movie Carlito's Way, five years after drug dealer Carlito Brigante is sent to prison for murder, his lawyer gets him out because of prosecutorial misconduct and illegal wiretaps that led to the evidence being tainted. The judge that ordered Carlito's release made it quite clear this was the only reason he released him and deeply regrets having to do this (especially since it was the same judge who presided over his trial to begin with).
In Superman Returns, Lex Luthor had his conviction from the previous Superman movie overturned because Superman didn't show up to testify against him in the appeal. There is no testimony in appeal hearings; only the trial record is reviewed, making this a research flub, as Luthor clearly said he got off because Superman didn't show up to testify at the latest appeal. The reason for this was that Superman had left Earth to follow a false lead regarding the remains of Krypton. The false lead was somehow engineered by Luthor himself exactly for the purpose of getting off on that technicality.
Well it could have been a motion for a new trial, which can involve testimony. This isn't usually termed an appeal, though.
There's Something About Mary: Mary's architect friend, who was actually a pizza delivery boy, claimed Pat was a murderer who stayed in prison for five years until a technicality got him off. The claim was false.
Honor Harrington: In The Short Victorious War, Harrington learns the reason Young was not removed from command after the events in “On Basilisk Station”. He used a loophole to give his return to the shipyard for repairs a legal basis.
In the fourthHarry Potter book, it was revealed that, when Lord Voldemort murdered his muggle father and his father's parents, the Muggles believed Frank Bryce, the caretaker of the mansion where he lived, committed the murders. Bryce was not charged because the forensics experts failed to establish a cause of death - the Killing Curse doesn't leave signs that can be noticed without magic - but the villagers remained sure Bryce was guilty... somehow.
In the H. Beam Piper story "Lone Star Planet", set on New Texas, the new Solar League ambassador, Stephen Silk, has to arrange this for the three men who assassinated the last Ambassador. The logic was that on New Texas, politicians are defined as literalAcceptable Targets - you're only punished for killing a politician if the court's opinion is that said pollie didn't have it coming - and this specialized court was the venue for the assassination trial. However, defining ambassadors as practicing politicians would lead to some very awkward precedent, meaning that Silk has to first build a conclusive case around them, then remind everyone that it's the wrong court, and New Texan double jeopardy laws meant there couldn't be a retrial. Of course, since it's a cowboy planet, you can freely carry guns into court unless you're the defendant, and after the verdict of "technically not guilty and it's a damn shame" is handed down, Silk proves that there's no technicality that will get you off a bullet through the head by gunning down all three at once. Quoth the judge: "Court-is-hereby-adjourned-until-0900-tomorrow-hit-the-deck!"
The district attorney in the book version of Clear and Present Danger takes pride in the fact that he has never lost a case on technical grounds. This is not the same as never losing a case ever, but is still impressive.
One minor character in the Tim Dorsey novel Florida Roadkill got himself and his friends off on a technicality when they were arrested for drunk driving and possession of alcohol when they were in high school. He found an obscure law that proved that the officer who arrested them didn't have valid grounds to pull them over, and since all further evidence was taken from a technically illegal police stop, it was inadmissible in court. He wins the case and grows up to be a DA.
In Artemis Fowl Mulch Diggums is released from prison after the eponymous character has tampered with the police's records, making it look as if the first search of his home was carried out before it was ordered.
An episode of Walker, Texas Ranger had three cops giving Vigilante Executions to criminals they feel didn't get the punishment they deserved. One of the people they kill is a kid who was actually innocent; DNA evidence exonerated him, but the cops never checked.
Adam-12 and Dragnet: Both Jack Webb-produced series featured Courtroom Episodes where suspects had charges dropped on various technicalities – key witnesses fail to show, obtaining evidence without a search warrant... the list goes on.
Babylon 5: Legally gray/grey tactics are used for political and/or personal reasons.
In "Point of no Return", Sheridan uses a 'chain of command' irregularity to prevent Nightwatch taking over the station. They certainly consider Sheridan to be a criminal getting off on a technicality.
In an episode of All in the Family Archie Bunker is on trial after a policeman Archie called to report a mugging found a can of tear gas in Archie's home despite the latter not having the necessary license. During the trial, Archie asks what happened to the criminal who originally mugged him and the judge replies he was released due to him having had his Miranda rights read to him in English despite him not being a native English speaker. Gloria is then shocked at the thought of the criminal being released and her innocent father being jailed... until the discussion brings to light the fact that the officer who found the tear gas didn't have a warrant, which causes the case to be dismissed. The judge then states the episode's Aesop that despite the justice system not being perfect and sometimes letting criminals go free, it ensures that everyone's rights are respected.
The first being classic Hollywood Law, while the second might be too, if the tear gas was in plain sight when the police officer saw it.
Judge Nicholas Marshall, the protagonist of Dark Justice, became a vigilante when his wife and his daughter were murdered and their killer got off on a technicality.
Dexter often hunts down killers who got off on a technicality, along with killers released from jail and ones the police never tracked down.
The ABC series Hardcastle and McCormick featured a retired judge (Brian Keith) who set out to bring down criminals who were released on technicalities.
In the final episode of Homicide: Life on the Street, Bayliss discovers that Luke Ryland, a child molester he'd arrested earlier in the series, had been released because court backlogs had delayed his trial so long that the case was thrown out (on the basis that, at least prior to 9/11, you couldn't just detain someone indefinitely without trial). At the end of the episode, Bayliss quietly packs up his desk and leaves the department, just as two of the other detectives discover the body of Ryland.
A whole episode of the old cop show Hunter was based on this, when a group of kids spontaneously confessed to killing a girl at a party, before the cops even had a chance to read them their rights. This sparked a vigilante-kills-the-killers plot. In Real Life, the technicality wouldn't have applied in the case of a spontaneous confession, and the police could then investigate to find other evidence that would support this.
In an episode of The Practice, a man was found with his wife's body in the trunk of his car. However, because the female cop in question was unable to give a reason to search the car's trunk, the search was ruled inadmissible, and the body (and all the evidence on it) was ruled to be fruit of the poisonous tree. However, it turns out that the cop and the man had planned the improper search between them; they'd been having a relationship for some time. The "vigilante justice" aspect happens when the man's lawyer finds out about it, and "accidentally" lets it slip to the ADA, who happens to live in the same apartment as his partner. Since he gets the answering machine, and presumably knew his partner wasn't home and the ADA was...
In one episode, Lindsey uses a botched search to argue for the release of a nun-killer. She gets him off, but feels awful about it.
Mr. Chapel in Vengeance Unlimited often hunts down killers who got off on a technicality, along with killers released from jail and ones the police never tracked down, but his net is wider, he doesn't kill his target, and he only does it for a million... or a favor.
In an episode of Frasier, Martin tells Frasier about an incident where he was arresting a man with a long criminal record, and was attacked while reading him his rights, meaning that they weren't read in full. Martin says that when it came time to testify in court whether the man had his rights read in full, Martin lied that they were so he wouldn't get off on a technicality. He justifies it with the fact that the man had been arrested so many times that "he could have read me my rights" and that it was the right thing to do (since the man was a violent criminal).
Even worse is that there would have been no reason for Martin to lie. The man assaulted a police officer. The officer (just like anybody else) is legally perfectly able to testify about a crime if he's the victim, Miranda warning or no. Plus, the arrestee interrupting his Miranda rights by assaulting the reader and attempting to escape is his fault if they weren't read correctly. On top of everything else, Martin says he "saw him shoot someone." Miranda Rights or not, he can testify and convict the guy, except maybe if there were a confession involved—only then if they weren't read before that would it be excluded.
On The Sopranos, after Dr. Melfi is raped, her rapist is immediately arrested and then set free on a technicality. In the end, the doctor chooses to allow him to remain a Karma Houdini rather than call in some Soprano Justice.
The gang from Angel actually deliberately sought this once for an obviously guilty human trafficker, as he threatened to mystically release a virus that would wipe out California if convicted. They succeeded by giving Gunn a large brain zap of legal information, allowing him to discover a potential conflict of interest involving the judge in the trial, forcing a mistrial.
One episode of The Rockford Files featured Jim getting out of jail on a contempt of court charge due to issues with the subpoena that was used to get him to testify in the case where the charges occurred. It listed the wrong middle initial.
"Juvenile": A suspect cannot be tried as an adult because the murder took place before the law allowing minors to be tried as adults was passed and she's way too old to be tried in Family Court.
Just as frequently, L&O would invert the trope; getting damning evidence in under technicalities. One example would be a letter written by the psychiatrist of the defendant to the victim warning her of danger was ruled inadmissible due to spousal privilege (as the psychiatrist was counseling both as husband and wife). But since they were legally separated at the time, Jack McCoy was able to argue that spousal privilege was void, making the wife a third party to the sessions, thus voiding doctor-patient privilege, thus letting the letter back in and nailing the defendant.
A sexsomniac mistook his fiancee's sister for his fiancee while "sleepwalking" and the DA can't charge him with rape because he wasn't conscious of what he was doing and he regularly had consensual sex with his fiancee in his unconscious state. It's Hollywood Law since his culpability would still be a matter for a jury or judge to decide (the DA acted like his condition was a 'get out of jail free card').
An alcoholic blacked out to find he'd killed the woman he had a one night stand with. The DA bungles the case, first by accidentally showing a reconstructed video of the crime with his face tacked on instead of the video with the faceless model, then by showing up drunk to the hearing to determine if the case should be thrown out on her misconduct. She has to suffer through having the drunk test performed on her in the courtroom and fails, which results in her dismissal and sanctions.
A murderous schizophrenic nutcase got his case thrown out after the overenthusiastic lab tech Dale Stuckey mis-labeled his DNA sample. The episode's plot leads into a whole other direction near the end before the audience finds out if the cops got him on holding his lawyer hostage. Stuckey later turns out to be a crazed killer himself.
A case of a Karma Houdini occurred when a character who committed an outstandingly heinous (even for this show!) double murder, during which he buried a baby alive, got off because before he confessed and led the detectives to the corpses while waiving his right to counsel, he mentioned that he had an upcoming burglary case. Because the mention of the burglary case was an offhanded comment in the middle of a conversation, and the suspect didn't draw any attention to it, the detectives did't connect that the upcoming case meant that an ordinary waiver of counsel wasn't enough, and so the judge ruled that the confession and bodies are inadmissible. Unlike the other examples from SVU, this was a deliberate plan by the suspect rather than a bit of good luck brought about by a spectacular Idiot Ball from the detectives.
On The Mentalist, there was an episode featuring a man who was accused of murdering his wife and only wasn't convicted because a videotape proving that he lied about not being at the crime scene when it happened was ruled inadmissible for not being presented on time. It was revealed later that the man was really innocent and that the real murderer doctored the tape to frame the victim's husband.
It is later revealed that a number of criminals caught by the team were later released because the evidence against them was deemed tainted due to Jane's antics during the investigations.
In the live-action Batman series, Batman was a deputy and sometimes even acted as a prosecutor. Despite this, no enemy of his ever tried to convince the judge to dismiss evidence that only came into light because of Batman breaking into places without a search warrant (that would be admissible if he wasn't a deputized police officer).
Or trying to get Batman disqualified as prosecutor. Is "Batman" licensed to practice law in whatever state Gotham is located?
On the The Closer episode You Have the Right to Remain Jolly, "Santa" starts confessing things before Flynn has the chance to Mirandize him, and they're afraid this might happen. Luckily, he's had a lot of egg-nog and ends up passing out and hitting his head on a table, so when he's sobered up a bit, they can read him his rights then and talk to him again. And also, he didn't do it.
In the first episode of Tales from the Crypt, "The Man Who Was Death" one murderer gets off free because the arrest warrant was improperly signed, leading the protagonist to later hunt him down and electrocute him to make sure he doesn't escape punishment.
In a Harry Potter fanfic titled "Growing Up Black", years after Sirius Black was sent to Azkaban, some of his relatives started having doubts about his guilt, decided to check the facts and found out he wasn't allowed to have a trial. They got him free by invoking a law stating that no pureblood can be forced to spend more than one month in Azkaban without a trial and that all charges against purebloods who are forced to stay more than that time there must be dropped. Sure, he's innocent, but since this is not what got him off, it can arguably be counted as a technicality.
Actually, while the law invoked to get him free was supposed to work regardless of Sirius being guilty or not, the relative who brought the case to the Wizengamot did point out reasons to doubt his guilt before invoking the law. However, people who don't believe Sirius Black's innocence usually say he got Off on a Technicality. It doesn't help that his family had to pull some strings just to have a chance to plead Sirius' case.
In another Harry Potter fanfic, "My Parents' Secret Keeper", Sirius Black did get a trial and was acquitted but, since the Wizarding World believed him to be guilty, he wasn't allowed to take Harry away from the Dursleys. In that fic, the Fidelius Charm leaves a magical trace on the Secret Keeper and Sirius Black had no sign of that trace, which got him acquitted from the charge of being the one who betrayed the Potters to Voldemort, despite everyone being sure the only reason he had no sign was that, with James and Lily dead, the trace had vanished. And Sirius couldn't prove his innocence on the mass murder charge because there were no witnesses (the wizarding world believed the lack of witnesses to be the reason he wasn't convicted). Years later, after Harry's second year at Hogwarts, Sirius found a law that allowed him to take custody of Harry. Unfortunately, Harry was so convinced of Sirius Black's guilt he refused to listen to his Godfather's pleas of innocence until Peter Pettigrew showed up and almost killed Harry in an attempt to get Sirius finally convicted of something. Peter wouldn't feel safe living as somebody's pet rat with Sirius free to look for him.
In "These Grim Bones", yet another Harry Potter fic portraying Sirius Black as a Death Eater who got Off on a Technicality, Cornelius Fudge, wanting to conceal the fact that (in the fic) some of the Muggles allegedly killed by the explosion actually fell victims to blunders from Obliviators, convinced most of the Wizengamot members to pass a motion to have Sirius only answer questions regarding his guilt or innocence of the crimes he's been charged with. Fudge's official excuse was that, even under Veritaserum, Sirius could twist the truth to the point of getting himself acquitted if he ever got a chance to give elaborate answers. After Sirius claimed under Veritaserum that he didn't betray the Potters to Voldemort, didn't kill the Muggles and didn't kill Peter Pettigrew, Albus Dumbledore accused Sirius of being able to overcome Veritaserum and tried to have him convicted on the remaining evidence but failed because it was Dumbledore himself who said Veritaserum would be needed to settle any doubts. That and the fact the Wizengamot wouldn't go back on the ruling of having Sirius answer only the basic questions got him acquitted but still believed to be guilty.
In Hank Williams, Jr.'s song "I Got Rights", this happens at the trial of the man who murders the singer's wife and son.
Happens in the back story for Ace Attorney Investigations, where Manny Coachen is cleared of murder because the prosecution suspiciously lacked the evidence they used to arrest him. And by suspiciously lacked we mean the smuggling ring stole it right before the trial.
In the sequel, one killer happily admits the deed... after the statute of limitations on the case has run out. Subverted when he gets arrested due to another technicality; because he fled the country, the statute of limitations got extended long enough to still be in effect.
Hitman: Contracts, where the Meat King got off on a technicality for murdering your client's daughter. The "technicality" is implied to be some form of bribery.
Used by the weapons smugglers in the two-parter Two-Face, where Dent begins his slide into insanity. However, since this takes place in Gotham City, it is certainly a case of bribery and a corrupt judge.
Also appears in "Trial": new district attorney Janet van Doorn can't give Poison Ivy a life sentence since Batman brought her in and not law enforcement agents; the judge claims to only be able to throw her back into Arkham for the remainder of her rehabilitation sentence.
South Park: To avoid being arrested for illegal hunting, Jimbo always claimed his game was about to attack him. When a new law made it impossible to use that excuse, Jimbo started claiming he was reducing the animal population to save the whole bunch from starving to death.
Inverted in an episode of The Simpsons which has Homer's mother sent to prison on a "technicality" (having committed a petty crime on top of those she'd been convicted and pardoned of), and Homer exclaims "People should only get sent out of jail on technicalities!"
In "Stop or My Dog Will Shoot" Santa's Little Helper as a police dog catches Snake who then gets off on a technicality.
Judge Snyder: I'm afraid because of this improperly filled out police report... * shows a report full of paw prints* ...I have no choice but to let you go. Case dismissed!
Snake (to Santa's Little Helper): Haha! Don't worry, dude. I'm going straight. Straight to my customers to sell more drugs!
Santa's Little Helper: Grrr...
Sideshow Bob tries to pull this off when he kidnaps Bart with the intent to kill him at "five corners", (a fictional location where five states come together). His plan is to stand in one state, fire the gun in a second, the bullet travels through a third, hits Bart in the fourth and he falls and dies in the fifth. Bob thinks it would be impossible to convict him because no single act in any state would be illegal. He's completely wrong. In truth, he could be convicted of murder in any of those states (police from each of them arrive and arrest him simultaneously).
In Spider-Man: The Animated Series, the Prowler was a minor street thug whose lawyer got his case thrown out since Spider Man apprehended him but wasn't present to testify as to his guilt. Why Mary Jane couldn't ID him as the man who robbed her is never asked.
Teamo Supremo once faced a criminal said to have used a technicality to get away with previous crimes.
One UK lawyer makes a very nice living getting the rich and famous off traffic tickets, speeding, drunk driving etc, exactly on this.
That whole Supreme Court case about whether it violates the separation of church and state to have kids saying "under God" in the Pledge of Allegiance at school ended very boringly when the Court ruled that since the father who filed the lawsuit didn't have custody of his kid, he couldn't claim to be protecting her First Amendment rights.
A great many cases the judges don't want to decide (that is, political cases) are dismissed when the judges rule that the person bringing the case doesn't have standing to sue. This is especially true when the judges know (as in the above case) that their decision would be hugely unpopular (or alternatively, that they don't want to make the correct ruling because they like the status quo, even if it's wrong).
Even if you can prove that the government illegally spied on you, the feds will try to have the entire case thrown out on "state secrecy" grounds. Even if some of the evidence you have isn't secret.
In evidence involving government spying, they can legally conceal the "sources and methods."
The Scopes "Monkey Trial", over the teaching of evolution in schools. Scopes's conviction was set aside on appeal: the Butler Act, forbidding the teaching of evolution, carried a mandatory fine of $100, which is what Scopes had been fined when convicted. However, Tennessee law of the time forbade judges from setting fines above $50, rendering the judgment invalid.
Not to mention the entire trial was a fabrication to save the town of Dayton, Tennessee by putting it on the map, bringing tourist dollars in-Scopes hadn't even violated the law, only going along with it for this purpose.
Very often, technicalities (for example, improperly collected evidence or confessions) will result in a retrial with said data excluded, not a defendant "getting off scot-free". Ernesto Miranda himself was convicted on retrial, and went to prison (though he was paroled in only three years).