Guilt by Coincidence

A highly publicized crime has just been committed, with the criminals bearing distinguishing marks that make them easy for the general public to recognize if they see them out on the street. Unfortunately, those distinguishing marks are also generic enough for anyone who has similar features to be mistaken for the criminal.

Usually, when this happens, the person(s) who mistook the innocent person for the perp will overreact, and either call the cops and/or go after the suspect themselves. Or, in a similar vein, the mistaken-for-perp performs an action that, to a police officer or passers-by, seem suspicious and paramount to guilt in the crime, even though in reality the action was meant to be innocuous or even helpful to the situation. Either way, Hilarity Ensues... unless played straight, in which the victim of the mistaken identity is either beaten to death by a vengeful mob or wrongly imprisoned.

A more general superset of Mistaken for Murderer.

The trope name comes from the old saying "Guilt by association", which itself invokes the real-life charge of accessory to the crime.

Comic Books

 * Watchmen: Nite Owl is a Legacy Character. The original Nite Owl went public and wrote a book after his retirement from being a superhero. The current Nite Owl, whose identity is never publicly known, helps break Rorschach out of prison during a prison riot. A street gang wants to get revenge on him for that and they.
 * In the original Teenage Mutant Ninja Turtles comics, April and the turtles once got chased by the police because April's van coincidentally was the same make, model, and color as a van used by a group of bank robbers earlier that day.

Film

 * In M, the scare over the child killer is so great that one completely innocent man gets attacked by an angry mob just for speaking to a child. Part of the premise of the film is just how useless the common folk can be.
 * Vigilantism was something that bothered M director Fritz Lang; his first American film, Fury (1936) stars Spencer Tracy as an innocent man who's nearly killed by a lynch mob-- but in what could be a case of He Who Fights Monsters, he attempts to frame the entire mob (or at least the 22 people shown in newsreel footage of the crime) for succeeding in his murder.
 * Hitchcock's The Wrong Man.
 * In Master of the Flying Guillotine, the eponymous villain goes on a vendetta after a one-armed boxer killed his disciples, murdering every one-armed man he stumbles across.
 * Inverted in Out of Time. An older white woman who was a witness to a crime describes a black man to a sketch artist and then points out the chief of police (and, coincidentally, the man she saw at the crime scene) as being the culprit. After a tense pause, she starts pointing out every black man in the station which discredits her testimony, and marks one of many close calls for the protagonist while he tries to slow down the investigation that is leading straight to him.
 * V for Vendetta had V send copies of his mask to virtually the entire population of London. State Sec overreacted when children started wearing them, resulting in even more of a backlash from the people against the government.
 * A 1940 Batman serial really goes over the top with this. The masked villain gets a distinctive cut on the back on his hand while getting away...and suddenly three major characters are sporting them, and the mystery of who he is is kept alive a bit longer.

Literature
"There were, of course, mistakes.
 * Wheel of Time: After Rand announces himself as the Dragon Reborn, it's mentioned that anyone in the area who is remotely similar to his description (young, male, red hair, tall) is at risk of being attacked.
 * In the Sten series, there was operation Nightfog, a purge of military personnel who'd been conspiring to bring down the Council which usurped The Empire:

A writer of children's fiche named White, much loved and respected, was unfortunate to live in the same suburb as a retired major general named Whytte. The writer's house was broken into in the middle of the night. The writer was dragged to the center of his living room and shot. The writer's wife tried to stop the killers. She was shot as well.

When the mistake was revealed, the head of the murder unit ... thought the matter an excellent joke."


 * In A Song of Ice and Fire, after, Cersei offers a huge reward to anyone who brings her the head of her dwarf brother Tyrion, which leads to a steady stream of people bringing her the heads of innocent dwarves and the occasional child. The murders go unpunished because Cersei doesn't want anyone to hesitate if they actually do find Tyrion and aren't entirely certain of his identity.

Live Action TV

 * An episode of CSI involved the beating death of a taxi driver by an angry mob after he supposedly ran down a young kid. Not only was the kid already dead when the taxi rolled over him, but the driver -- whom the mob assumed was getting back into the taxi to drive away -- was actually reaching for his CB radio to call in the accident.
 * Justified in an episode of Drake and Josh -- Josh not only resembles the Theater Thug, he was hired to play the criminal on "America's Most Wanted". Is it any wonder people kept trying to get him arrested?
 * But for the police to arrest him
 * There was a TV Show on PBS a while back about thrift stores and other ways to get cool used stuff. To start the journey, the show's hosts bought a retired ambulance on eBay to cart their findings around in. Several weeks into production, some terrorists stole an ambulance. Within a month, they had been pulled over by, interrogated by, and gotten signed statements from troopers in at least three states attesting that it was not these guys. Not that any of the troopers believed the previous ones, of course.
 * In many Doctor Who stories, the Doctor arrives in an environment (e.g. research base, spaceship, space station) shortly after sinister events have begun occurring, usually including deaths. The person in charge (e.g. commander, director of research) assumes the Doctor and companion/s did it. (Admittedly, under the circumstances, that's often not so unreasonable.) Then the Doctor and companion/s are opposed by the people they're trying to help, as well as the actual villain/s.
 * A fifteen year old boy (at the time) in Flashpoint was accused and sentenced for raping and murdering a classmate of his, being the last person to see her and
 * One episode of The Mystery Files of Shelby Woo, Shelby and friends were trying to figure out who stole jewelery from a safe and became very suspicious of a magician who the spotted trying to conceal a small box on the porch. Once confronted, he began looking very guilty and his wife started to cry. Turns out he was on a diet and was sneaking food behind her back.

Real Life

 * Any young person who wears a trenchcoat nowadays is more often than not accused of being part of the legendary "Trenchcoat Mafia", a presumption made famous from the (equally erroneous) accusation that the perps in the Columbine High School shootings were part of the gang (which the Trenchcoat Mafia technically were not).
 * Today? As in 2010? Because at my school, we just assumed they were Matrix fanboys.
 * Occasionally, it's been reported that actors that work for shows like Unsolved Mysteries and America's Most Wanted have the police called on them by people who, having seen the reenactments, presume they're the criminals they're portraying.
 * This happened often enough that America's Most Wanted started notifying the authorities in the area where the actors lived so that they wouldn't get arrested.
 * Lets not forget the good old Paedophile witch hunts in the UK no so long ago, resulting from the publication of a sex offender list in a national newspaper. It was unfortunate for those who had similar names or addresses to the accused.
 * Not to mention the female doctor whose house was subject to an arson attack because people in Gwent apparently don't understand that there is a difference between a paediatrician and a paedophile.
 * That's an urban legend/exaggeration. Her house was graffitied with the word "PAEDO," probably by neighborhood teens. The idea that the perp(s) didn't know the difference between "pediatrician" and "paedophile" was a guess made by police. The bit about the anti-pedophile arsonists comes from a case in Portsmouth with a real pedophile (but the vigilante acts were still unjustifiable). Somebody conflated the two news stories (both from August, 2000), and the oft-quoted version was born.
 * This has been repeated of late with the "No Fly" lists in the US; people who are so dangerous they cannot be let on a plane under any circumstances, yet haven't actually done anything bad enough to warrant investigation or arrest. If you shared a name with someone on that list, flying would take on a whole new dimension of fun.
 * And the best way to get off that list - legally change your name. It works even if it's really about you and not somebody you share a name with. Someone in the Homeland Security apparently seems convinced that terrorists are too honest to use false names.
 * My brother shares a name with someone on that list, and all he's ever had to do is buy a ticket using his middle initial.
 * People have also been kept from voting in certain states if their name was similar to one on a list of convicted felons. This was one of the controversies with the Florida ballots in the 2000 presidential election.
 * This is supposedly why the Gunman with Three Names trope exists -- to prevent people with two out of the three names of the killer from being accidentally arrested or victimised.
 * Journalism students - at least in this troper's class - are taught to be very specific about accused criminals with generic names, adding either an address or middle initial.
 * During the famous Beltway Sniper attacks, pretty much the only evidence the police had to go on was that a white van was seen at the crime scenes. People immediately started to report every time they saw a white van; it's actually been suggested the flood of false leads hampered the case.
 * Interestingly subverted in the same case. This Troper recalls many news stories where, with no real evidence to report, people continually mentioned that the culprit(s) would probably fit the usual profile of a serial killer: white, male, about thirty and with no real motive other than psychopathy. Instead, it was two black Muslim men, one of whom was a minor, doing it to cover up the eventual murder of the older man's wife -- which they were apprehended before committing -- as part of a series of random killings.
 * It's also notable that they *weren't* shooting from a white van, but from a blue Chevy Caprice car.
 * On September 5, 1921, Silent Films comedian Fatty Arbuckle was giving a party in a San Francisco hotel room when actress Virginia Rappe's uterus began to hemorrhage. She died four days later. Arbuckle was charged with murdering her. (It's been theorized that her uterus hemorrhaged due to several back alley abortions.) Unfortunately for Arbuckle, Mary Pickford's sister-in-law, Olive Thomas, had accidentally ingested a solution of bichloride of mercury on September 5, 1920, and died five days later. (Thomas's husband, Jack Pickford, had syphilis. Bichloride of mercury was then commonly used as a topical treatment for the sores.) The fact that Rappe fell ill on the one-year anniversary of Thomas's accidental poisoning did not go unnoticed by the Moral Guardians of the time. The scandalous deaths of Rappe and Thomas and several other silent film stars in the early 1920s were among the factors that led to the adoption of the Hays Code in the 1930s.

Theater

 * In both Shakespeare's play Julius Caesar and in reality, Cinna the Poet was murdered by a mob due to his shared name with one of Caesar's assassins. This was ironic, historically, as he was a friend and supporter of Caesar, but Shakespeare introduced some black comedy by having a member of the mob comment that even if this Cinna isn't the guilty one, being a bad poet is reason enough to kill him.
 * This was something of a Take That Me in the original production, where Cinna the Poet was played by Shakespeare himself.

Western Animation

 * This happens to Groundskeeper Willie in The Simpsons episode The Great Money Caper.
 * In an episode of The Boondocks, Tom, a criminal prosecutor, is arrested for supposedly resembling the X-Box Killer.