Off on a Technicality

""I punched some jerk in Tahoe; they gave me one-to-three, My high-priced lawyer sprung me on a technicality, I'm just visiting Springfield Prison; I get to sleep at home tonight.""

- Krusty the Clown, The Simpsons, parodying Johnny Cash

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.

Most prevalent back in the 1970s and 1980s with the vigilante justice fad in fiction, after several court decisions seeming to tip the balance of the legal system in favor of the accused. In Real Life, police and other law enforcement personnel are carefully trained to avoid screwing up their cases like this, and the fictional versions have become rarer.

In a Police Procedural, such as Law and 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 to replace the botched info.

In stories where a Vigilante Man or Cowboy Cop is the protagonist, the legal system is seen as more concerned about "procedure" than "justice," and Strawman Political bleeding heart judges will accept any half-baked excuse for letting criminals go free. (This is often a case of Did Not Do the Research where in Real Life the technicality wouldn't have been applicable.) 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.)

The Amoral Attorney with Rule Fu Stronger Than Yours loves taking advantage of this.

Anime & Manga

 * The Magnificent Bastard Big Bad Gouda almost gets off with this in the second season of Ghost in the Shell.  Something of a Chekhov's Gun, since the same law was brought up in an earlier episode.
 * The reason he nearly gets off? Apparently in Ghost in the Shell-world simply turning yourself in absolves you of all responsibility for your crimes, even when said crimes involve ,
 * Which would explain why the Ghost in the Shell world is a bit of a Crapsack World. In addition, there are multiple storylines involving a Treachery Cover-Up.

Comic Books

 * 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.
 * A semi-regular occurrence in Batman comics, because it's Gotham.
 * Happened thrice during Jason Todd's short tenure as Robin, which may explain why the kid became tempted to take the law in his own hands.
 * The man who shot Commissioner Gordon during the Officer Down storyline walked free. His death isn't so much made look like an accident as like his old associates got the leak on his Witness Protection identity.
 * 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, of course, 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 or officers of the court. Even if the private citizen broke actual laws in the process of obtaining the evidence, the evidence is still useable in any court; the only effect of said illegality is that the evidence-obtainer is himself liable on his own set of criminal charges.
 * 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.

Fan Fiction

 * 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 with basis 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.

Film

 * 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 evidence on that case, but certainly not for Scorpio's attempted murder of Callahan, assault with a deadly weapon, possession of a (likely 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.
 * Scorpio can still be physically identified by Harry despite the balaclava (by voice, and by the fact that Scorpio has a knife wound identical to the one Harry inflicted on the kidnapper). Furthermore, Harry's warrantless search of Scorpio's room, although technically illegal by current law, would have been legal under case law at that time—as a person unlawfully squatting in a business property (the stadium), by 1972 law Scorpio has no reasonable expectation of privacy, therefore a warrant is not required for search and seizure.
 * Also, identification by voiceprint started being used for police forensics in 1967.
 * 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.
 * Lethal Weapon 2. This is a running concept throughout the movie that the Big Bad and The Dragon are foreign diplomats who can't be arrested or prosecuted over any offence in the United States due to diplomatic immunity. In Real Life, most governments would at least expel diplomats who were proven to be heroin smugglers. Of course, it doesn't turn out well for them in the end.
 * In the A Nightmare on Elm Street series, child-killer Freddy Krueger was said to have been let off on a technicality, so the parents of Elm Street banded together and burned him alive. A case of Did Not Do the Research, as these articles 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.
 * Freddy Vs Jason Vs Ash The Nightmare Warriors also presents another possible reason for why Freddy managed to walk - a time displaced FBI agent (long story) impulsively tampered with his file and the paperwork within.
 * 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 a child murderer's 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.)
 * Played for laughs in Liar Liar,
 * In the Al Pacino movie And Justice for All, the character Jay has a nervous breakdown when a man he got off on murder kills a couple children.
 * 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 Face Palm-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. The judge that ordered Carlito's release made it quite clear the prosecutorial misconduct was the only reason he released him and deeply regrets having to do this.
 * 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 on criminal appeals; only the trial record is reviewed, making this a case of Did Not Do the Research, 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.
 * There's Something About Mary: Mary's architect friend,, claimed Pat was a murderer who stayed in prison for five years until a technicality got him off..

Literature

 * 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.
 * Specifically, if all of a ship's senior officers testify in writing that a starship requires emergency repairs, then regulations require that it return to the shipyard ASAP for emergency repairs. Even if it could actually have gone months more before needing maintenance.
 * In the fourth Harry 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 literal Acceptable 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 specialised 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.
 * 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 same 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.

Live-Action TV

 * Babylon 5: legally gray/grey tactics are used for political and/or personal reasons. They are never used to promote justice.
 * 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.
 * This also shows ignorant use of the Miranda rights, as shown elsewhere in the page. Was the canister in plain sight when the officer presumably came inside? If so, that should be valid.
 * IIRC the canister was in a closet that the cop just happened to open. Silly, I know.
 * It was in a drawer in their living room and the officer only started looking for it after Archie told him about during his explanation of the mugging.
 * In which case he had him dead to rights.
 * 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.
 * From the judge's own court—even though it is the judge himself who rules on such technicalities. (While it could be argued that the judge was strictly following the letter of the law despite his personal misgivings, and/or the convictions were overturned on appeal, that's not what the show's Opening Narration implies.)
 * It is likely that Judge Hardcastle is going after criminals who had their convictions from his court reversed on appeal.
 * 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 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; likewise even if the confession were excluded, this would not have the ridiculous effect of letting the suspects go scot-free, or have any other effect.
 * 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 fruits of the poisoned tree.
 * In one episode, Lindsey uses a botched search to argue for the release of a nun-killer..
 * 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 to testifying 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 the suspect 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.
 * Now that is a technicality...
 * Law & Order as noted in the trope description, generally subverts this by the end of the episode or compensates with extreme prejudice. However, there are a few exceptions:
 * "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 counciling man 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.
 * But played straight in that there's no need to do this in the first place—unlike attorney/client privilege, doctor/patient privilege does not extend to concealing evidence of felony crime.
 * SVU has a few:
 * 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 both 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') and Hollywood Psych as sexsomniacs cannot premeditate sexual encounters with a specific person; the condition is based on them being completely out of touch with whom they're having sex with.
 * 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 hozed 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.
 * Realistically subverted, however; the murderer didn't get off entirely, but was granted a mistrial.
 * 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.
 * A particularly terrible 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 unadmissable for not being presented on time.
 * 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.

Videogames

 * Happens in the backstory for Ace Attorney Investigations, where Manny Coachen is cleared of murder due to the prosecution suspiciously lacking the evidence they used to arrest him.
 * In the sequel, one killer happily admits the deed... after the statute of limitations on the case has run out.
 * 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.

Western Animation
* Batman: The Animated Series: used by the weapons smugglers in the episode 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. "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..."
 * Inverted in an episode of The Simpsons which has Homer's mother sent to prison on a "technicality" (having committed petty crimes 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.


 * 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.

Real Life

 * 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.
 * If the US government has spied on you illegally and they classified the spying as secret, you can't sue. Because the fact that they spied on you is classified, you can't prove they spied on you. If you could prove it, you could sue, but the evidence is secret, so you can't.
 * 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." This is because there is another law forbidding the names of intelligence agents under non-official cover to be publicly revealed anywhere ever, and court proceedings are public record.
 * The Scopes "Monkey Trial", over the teaching of evolution in schools. Scopes's conviction was set aside on appeal: The Butler Act, forbidding 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.
 * An infamous political example: "I did not have sexual relations with that woman." A US President (Clinton) lying under oath is clear grounds for impeachment, but because the agreed-on legal wording during the deposition for "sexual relations" did not include oral sex, that charge failed. The joke at the time was "this is how you get off on a technicality". (Clinton was impeached for obstructing justice and a separate perjury charge, but acquitted by the US Senate).
 * The press conference quote is not what he was charged with perjury for—the charges were about President Clinton's sworn affidavit in the Paula Jones sexual harassment case (during which he also denied having sexual relations with Monica Lewinsky). However, since the *dictionary definition* of "sexual relations" did not include oral sex, his attorneys successfully argued that President Clinton's answer, while possibly misleading, was not actually untrue and that the blame lay on the prosecutor for not asking a specific enough question to avoid an ambiguous answer. That said, IIRC the agreed-on legal wording allowed her to be having sex with him while he was not having sex with her.
 * 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.
 * The Teapot Dome scandal is remarkable in that one man was convicted of bribing the US Secretary of the Interior, while in a separate trial the Secretary of the Interior was acquitted on charges of receiving bribes.