Everyone Is a Suspect

""They'll give statements and be eliminated, the rest of the Badge of Honor crew will be alibied, and then we'll only have the rest of Hollywood to deal with.""

- D.A. Ellis Loew, regarding the murder of "crusading reporter" (read: scandal monger) Sid Hugens in L.A. Confidential.

One of the key questions in detective stories is, who has a motive? Usually that only serves to narrow things down, as there are two or three people with a plausible motive, and even then a whole other person can turn out to be the actual killer.

But sometimes...well, the question is completely useless, as every single person in the general vicinity has a reason to want the victim dead. Not only was the victim a horrible human being whom everybody hated on general principle, but the victim also had specifically wronged all the other characters at some point. So, seriously, the killer could have been anyone.

Sometimes everyone's a suspect because Everybody Did It.

Long story short, its better to have lots and lots of suspects, because that it part of what makes it a mystery.

Anime and Manga

 * Oddly enough, since victims in Umineko no Naku Koro ni tend to be... just about everyone, just about everyone also winds up being a suspect. This helps to contribute to the drama, since Battler is trying to prove that the murders weren't committed supernaturally but doesn't want to suspect his family and friends.
 * Higurashi no Naku Koro ni leans towards this in the question arcs as well, as the narrator gets more and more Properly Paranoid about what the hell is going on.
 * Detective Conan has a few of these. Sometimes there is only one real suspect, who the audience knows is guilty because there is no one else (and Conan figures it out pretty quick too), and the question is how they did it. Then there are some episodes where you have a few suspects. Then some episodes that really define this trope.

Film

 * This was the premise of the film Drowning Mona.
 * Both parodied and subverted in the movie Murder By Death. The "suspects" are all of the guests and the house staff; with the guests consisting of parodies of many the most well-known literary and movie detectives -- Sam Spade, Charlie Chan, Hercule Poirot, Miss Marple, and Nick and Nora Charles -- all of whom had reasons to kill the host, which come up during the course of the film. The host is killed shortly after the guests arrive; after announcing that he will be killed, and offering scathing critiques of the various tropes and devices used typically used by said detectives, via their parody Captain Ersatzs. Subverted in that
 * Scream. It even has a character yelling the phrase "everybody is a suspect!".
 * Parodied endlessly in the Scream spoof Shriek If You Know What I Did Last Friday the Thirteenth:
 * All five major characters admit that they have good reasons why they would want to kill at least one of the other four, but none of them are the killer, who is hiding out right under the table they’re convening at.
 * Also, for no apparent reason both are wearing the exact same boots as the killer, while  has an exact match of the killer's entire outfit just lying around.
 * Boner casually mentions that he could kill all his friends if he wanted to, eliciting concerned or shocked looks on their faces. Then in a spontaneously upbeat tone he says that of course he wouldn't.
 * Dawson is accused of having killed his entire family, and.
 * The Thing creates its notorious sense of paranoia from this, though in this case it isn't so much "anyone could have committed the murder" as "any one of twelve men could in fact be a hostile shape-shifting alien capable of creating a perfect copy of people that it kills". Naturally, a good chunk of the plot is simply driven by the guys trying to figure out who to trust.
 * In A Shot in the Dark, Clouseau has assembled all the people in the mansion, and tells his tale in preparation for having the killer confess by trying to escape the room. When the lights go off, they ALL try to escape. Every single one of them was responsible for one of the murders in the movie (or prior to it), except for one who was a blackmailer.

Literature

 * Agatha Christie's Hercule Poirot novel Death on the Nile put the murder victim on a boat with seemingly everyone who hated her. It came so that the sufficiently Genre Savvy reader could figure out who did it, as there were only two characters who were cleared of the murder due to physical impossibility; naturally, they were our killers. And do we need to mention Murder on the Orient Express?
 * An interesting subversion is in the Miss Marple story A Pocket Full of Rye, where the actual murderer deliberately plots out the murder to tie in to the "Sing a Song of Sixpence" rhyme, which would incriminate (by chain of association) a brother and sister pair who had been told every day by their mother to wreak revenge on the murder victim who had wronged them in days of yore. Miss Marple concludes, correctly, that the siblings had much better sense than to waste their lives with revenge, but deduces that the sister did get back at the murder victim by marrying his son.
 * We can't forget The Murder of Roger Ackroyd. Readers of today can't imagine what a shock it was in 1926 to have the culprit of a detective novel turn out to be . The killer lampshades this trope in the end by admitting even they were confused by how much everyone else looked like they might have done it, and why their relatively straighforward crime was befuddled by contradictory evidence that seemed to show it could not have happened the way it really did- it turned out most of the suspects were lying or planting fake clues to hide their own secrets and crimes, which made them more suspicious.
 * Another good example is Cards On The Table whose plot is familiar to anyone who has seen the Clue film. A nasty guy invites a bunch of people to a party on the premise that all of them are scoundrels (in this case, specifically that they've all committed murder and gotten away with it) and pretty much blackmails them. Naturally, the host bites it, and there is a note at the beginning of the novel to the effect that all of them would be capable of murder if pressed. It is subtley implied that the eccentrice host is in fact Satan himself.
 * And who can forget the similar premise of And Then There Were None, in which ten people are invited to an island because they've all committed murder in such a way that they could not be blamed for it - deliberate neglect, emotional abuse driving a victim to suicide, sentencing an innocent man to death, etc. - and then killing them all off in the manner of the nursery rhyme?
 * In the novel Never Trust a Dead Man by Vivian Vande Velde, Farold - the murder victim - is terribly depressed to realize just how many of the people he knew have plausible reasons for wanting him dead.
 * In one of G. K. Chesterton's mysteries, various people try to consult the blackmailer during the day and come back claiming that he refused to stop fishing. In actuality, he had been murdered. Each one is cleared when it is revealed that they too had been his victims and so had been afraid that they would be accused.
 * This happens frequently in Michael Dahl's Finnegan Zwake books, particularly The Ruby Raven.
 * Marooned in Realtime uses this extensively. First, Yelen brings up dossiers of the entire human race sorted by means and motive (though at least one character insists on blaming hypothetical aliens). Later, Brierson deliberately makes himself a target to see which of the well-armed people attack him. Except for his partner, they all do.
 * In Boris Akunin's Seagull, not only Everyone Is a Suspect, but there's also an Alternate Ending for each suspect to be the culprit.
 * In Father, Forgive Them, numerous people were in the room when Dr. Curtland died, and admit to how much they would have liked to kill him, and that they had a means of doing so at the time. Predictably,.

Live-Action TV

 * A recent episode of The Glades had a murder victim who was a divorce attorney. The main character said it best: Half the state of Florida were suspects.
 * In episodes of Murder, She Wrote, you can usually guess who will be the first character to die: he or she will be the one systematically making every other cast member want him dead.
 * In every episode of the Clue TV series, it was explicitly set up so every character would have a reason to want the victim of the week dead.
 * Get Smart has an awesome recurring character who is a detective so thorough he considered himself a suspect until he finds evidence clearing his name.
 * Castle - "Everyone looks guilty to me, it's a job requirement."
 * Parodied; Beckett's words are echoed by Castle, in a much more dramatic fashion than Beckett's matter-of-fact statement, later in the episode. His daughter Alexis then points out that he just a minute before asserted that someone couldn't possibly have been a suspect. Castle, slightly peevishly, tells her to just let him have his moment.
 * The writers of this show love this trope. Sometimes it's an Asshole Victim, but sometimes it's just a perfectly normal person with very bad judgment in personal relationships. In one particular episode, it turned out that even though the victim was a more or less likeable person, her fiance, classmate, employer and client all had motives to kill her. The killer turned out to be.
 * In the Law and Order episode "Vendetta", Detectives Briscoe and Green investigate the murder of the in-story equivalent of Steve Bartman. Every fan of the relevant baseball team is a suspect.
 * In the Fight Club episode of Vampire Prosecutor, everyone in the club is suspected of killing the victim as they had battled him one after another, piling on the life-threatening injuries.

Theatre

 * The Mousetrap with rather predictable outcome.
 * Several characters in The Bat are suspected at one time or another of killing Dick Fleming.

Tabletop Games

 * In the board game Kill Doctor Lucky, the players compete with each other to be the one to finally finish the old man off.
 * The movie Clue had something similar--all the protagonists were Blackmail victims of the actual victim. Murder ensues ...

Video Games

 * When Team Fortress 2 fans finally meet the spy, he's introduced by way of a rather tense realization: Since nobody killed a Red spy on the way in, he could be in this very room.

Web Animation

 * Accuser: When a lawyer is found dead, one of the cops assigned to the case hinted that the victim's former legal partner might have something to do with that. When another one mentioned mentioned said partner's handicap (being wheelchair bound) as a reason to rule him out as a suspect, the cop who accused the victim's partner invoked the trope.

Western Animation

 * The "Who Shot Mr. Burns?" two-parter of The Simpsons developed motives for Homer, Bart, Smithers, Grampa, Moe, Barney, Skinner, Groundskeeper Willie -- basically, everybody in Springfield, as well as popular drummer Tito Puente. Marge even says the trope name at the end of part one. It then turned out that the shooting was an accident.
 * Burns did

Comics

 * A Far Side strip parodies this and The Butler Did It with a murder mystery that takes place at a butler's convention.

Real Life

 * The feudal lord of the small Spanish town of Fuenteovejuna was murdered in 1475. Since this happened during a Portuguese invasion of the region and the town was of strategic importance the Santa Hermandad put a lot of effort into the investigation of the murder, down to torturing several of the main suspects... yet they couldn't break any, and the only answers they got were pretty much that the guy was an ass, that everybody hated him and that the killer had been the whole Fuenteovejuna. The Catholic Monarchs accepted this explanation and pardoned the town. A fictionalized version of the incident is told in the 17th century play Fuenteovejuna by Lope de Vega.