The Killer in Me

""So it wasn't Dwight after all. Looks like I'm the killer. You never expect that you're the killer. It's a great twist. Great twist.""

- Michael Scott, The Office

A character (usually the main character, but sometimes sharing equal billing) is chasing or being chased by a killer or monster.

A lot of people end up dead, but not this character, and in the end we find out why: the 'hero' was the killer all along.

This can go one of two ways:

A) The 'hero' is a willing killer or monster who has been trying to shift blame or tie up loose ends.

B) The 'hero' somehow blacked out the murder(s) and is as surprised and horrified as the audience to discover the truth.

In many cases, this is essentially a Memory Gambit told In Medias Res.

When handled with care, it can be a powerful Twist Ending. When tacked on just for the sake of surprising the audience, however, it is likely that key events in the story will become illogical, or in the worst case, physically impossible.

See also Split Personality or Unreliable Narrator. In Speculative Fiction, this may be due to a Super-Powered Evil Side or Enemy Within.

Huge spoilers ahead of course!

Film
"Martin Vail: So there was no Roy. Aaron Stampler: No, Marty. There was no Aaron."
 * Perfect Stranger - Halle Berry's character murdered her 'friend' (who was blackmailing her) and successfully pins the blame on the innocent, if slimy Bruce Willis. Oh and she murders again when another friend tries to blackmail her about setting up Willis. This one is pretty much the result of last-minute Executive Meddling to decide the identity of the killer.
 * The protagonist of Dario Argento's Tenebre is revealed to have killed the murderer—an obsessed fan of his—halfway through the movie and then used it as a cover for a murder spree of his own.
 * One of the earliest movie examples: Forbidden Planet, via "Monsters from the Id."
 * Along Came A Spider - Monica Potter's character is the mastermind behind the kidnapping, who orchestrates the murders she is supposed to be investigating.
 * Kevin Costner's investigator protagonist in No Way Out, with the twist that, while he's not guilty of the murder he's investigating (and being framed for), he is guilty of being.
 * The (fake) FBI agents played by Bill Pullman and Julia Ormond in Surveillance.
 * The protagonists of A Perfect Getaway, are eventually revealed not to be in fear of the killers, but to actually be the killers. The other couples who are presented as potentially the killers are either their next targets, or stooges to pin the murders on.
 * The protagonist of Beyond Reasonable Doubt murdered a woman, covered it up, framed himself for murdering her (it made sense in context), got a mistrial declared, and finally was caught in the end.
 * In the french film Vidocq title character is a detective who disappears chasing mysterious murderer known as Alchemist. Vidocq's biographer Etienne takes up his investigation. Eventually, it turns out Etienne is the Alchemist himself, who tries to find and eliminate all clues leading to him that Vidocq left.
 * Aaron Stampler in Primal Fear, who reveals at the very end of the movie that his innocent persona was all a lie.


 * The Uninvited qualifies as this. In addition to being a Faux Horror Film, it turns out that Anna murdered every person that died. She doesn't remember anything she's done until a massive flashback scene. It also comes with The Reveal that her sister Alex has been Dead All Along.

Literature

 * Agatha Christie's The Murder of Roger Ackroyd.
 * The detective-narrator of William Weld's Mackerel by Moonlight.
 * Sort of. He's actually innocent of the murder he's accused of, but the twist ending reveals that
 * James Patterson's novel The Lake House does this; the beginning of the book says that the events are being told by the characters and may be inaccurate, but you're likely to ignore it until The Reveal.
 * Another of his novels does this as well.  Although this case combines a bit of part 2 as well.
 * Beach Road does it as well. It was so skillfully done too that if you aren't paying close attention, the end will throw you for a massive loop.

Live-Action TV

 * Used in season four of Angel: Cordelia was the Big Bad masterminding the events of the first two thirds of the season.
 * In one episode of Porridge, an elderly man in prison for murdering his wife years ago repeatedly protests his innocence. After eventually being granted a full pardon, he reveals he knows exactly what happened to the actual murderer: He killed him before being arrested for the wrong murder.

Music

 * The song "Buenas Tardes Amigo" by Ween appears to be about a man seeking revenge against his brother's killer, but in the end it is revealed that he did the deed out of jealousy, pinned the blame on someone else who promptly fled, and is about to seal the deal by killing the man he framed.
 * In the Vocaloid song "The Tailor Shop on Enbizaka", Sudou Kayo avoids mentioning that she was killing anyone by saying simply that someone was killed.

Anime and Manga

 * In Death Note, Light Yagami, who repeatedly insists that he is not the supernatural killer Kira, and does not remember being Kira, is Kira. Note however that this only applies during his Memory Gambit during the Yotsuba arc.
 * In the Higurashi no Naku Koro ni manga-only chapter Onisarashi-hen, viewpoint character Natsumi Kimiyoshi is responsible for the deaths of her family members, though she doesn't realize until the end due to Trauma-Induced Amnesia.
 * Also, in the first arc Onikakushi-hen, the main character Keiichi realizes that people around him are acting crazy and people are dying... He gets increasingly afraid, and kills his two best friends under self-defense. It wasn't. He was just being paranoid and delusional.
 * In Monster Inspector Lunge assumes this is Tenma's problem for pretty much the entire story because all the evidence he can find says Tenma is the killer.

Board Games

 * Most well-known in Cluedo/Clue, since the murderer could be any of the six Player Characters. Including yours, and you don't know if you did it or not (unless you've got your own card in your hand, or seen it in someone else's).
 * And, as amusingly pointed out in Murphy's Rules, if you deduce that you are the killer, you win the game by denouncing yourself.

Comic Books

 * Inverted in Alan Moore's Greyshirt comic, when a man finds himself with a bloody hammer and a dead woman, and no memory of either. He reads in the newspaper that the Hammer Killer has murdered eight people and flees the police as it must be him. But when Greyshirt and the police find him, they tell him he was the next victim: the Hammer Killer slipped while attacking him and broke her skull. Unfortunately, he has killed someone who tried to stop him, thinking he was a multiple murderer anyway.
 * An issue of Cable & Deadpool featured our favorite merc investigating a murder in Providence, his buddy Cable's brand new Utopia, only to have the investigation end with a two-page spread of Deadpool saying, "Now the only question is... why did I kill this man?!" It eventually turned out Deadpool's healing factor was interpreting traumatic memories as damage and healing them over, leading to periodic blackouts.
 * In Batman Two Faces Elseworlds, Bruce Wayne used a potion to transform into Batman who is the embodiment of all his good qualities. A mysterious killer who laughs started appearing and killing prostitutes and Batman chased after him. Only after investigation, it was discovered that he was the Laughing Killer who was the embodiment of all his bad characteristics.

Fan Works

 * Who can forget the line "No, John. You are the demons". What a twist!

Film

 * The Number 23 - Jim Carrey's character murdered his cheating girlfriend and suffered a guilt induced nervous breakdown causing him to forget the whole affair. The titular book was written by Jim's character (who wrote the rough draft), and his doctor (who fictionalized the story).
 * The film version of Secret Window - John Turturro's character does not exist; he is a schizophrenic hallucination undergone by Johnny Depp to commit acts (murder, arson) Depp could never consciously bring himself to do.
 * Shrooms - There are no ghosts or wild killers and Lindsey Haun (probably) cannot see the future; the mushrooms have driven her violently insane and she is the one who kills everyone.
 * Fight Club: Toward the end of both the novel and the movie,.
 * Used in Hide and Seek.
 * My Bloody Valentine 3D.
 * In the live action Dragon Ball movie, Goku finds out that the evil Oozaru, which he's spent most of the movie on a mission to defeat, is actually him. Somehow. Even though the Oozaru is supposed to be thousands of years old and Goku himself is only a teenager. It's not really explained.
 * Identity - Our "hero" turns out to be one of a serial killer's alternate personalities, and all the deaths in the movie are of various personalities inside the killer's head.
 * Haute Tension (also known as Switchblade Romance in the UK and High Tension in the U.S.) - The insane truck driver who ties up Marie's friend Alex and murders Alex's family... turns out the be Marie herself; the insane truck driver is her alternate personality. Alex, the film's true heroine, is abducted by Marie because of a suppressed lesbian attraction.
 * Spoofed in Adaptation: Donald's hackneyed script "The Three" has the twist that the killer, the detective, and the victim are all the same person. Charlie complains that it makes no sense, but it's a smash hit anyway.
 * This premise was made into a proper film called "Thr3e." The book it's based on is very popular among the (surprisingly large) Christian suspense fiction community.
 * Another similar film is the aforementioned Identity.
 * in Session 9. Also a Tomato in the Mirror.
 * The Uninvited.
 * Angel Heart detective Harry Angel is hired by Louis Cyphre to track down someone who skipped out on a deal with him, and is serious about it enough to kill to cover his tracks. The Shocking Swerve is that Harry is the missing person, had sold his soul to the devil, and has been killing to keep his disguise and therefore his soul.
 * Memento. The protagonist has frequent short term memory loss, and is trying to find the man who killed his wife. In the end, he accidentally killed his wife through an insulin overdose, and chose to preserve his sanity by rehearsing a story that it all happened to someone else, called Sammy Jankis. So now he chases criminals in revenge for an act he himself committed.
 * In Triangle,, who winds up killing all other characters (including herself) in doppelganger form, and is eventually revealed to be continually reliving the same sequence of events because she's a) insane, b) dead, or c) both.
 * The Gary Sinise film Imposter is an example.
 * The 2008 film Hide combines this with Tomato in the Mirror: The Villain Protagonist is the same person as the serial killer who abducted and has been torturing the protagonist's sister; when The Reveal is made, the protagonist kills his sister, then proceeds to torture his girlfriend in a Gory Discretion Shot..
 * In the 80s TV movie Blackout, Keith Carradine's character is in a car accident with another man, who dies. Keith loses his memory and is hideously disfigured. One of the two men is/was a serial killer, but no one, including Keith, knows which one. Until.
 * At the end of Blair Witch 2: Book of Shadows it is revealed that the three remaining main characters have been killing of their friends over the course of the movie, who they were hallucinating as evil people.

Literature
""There was another attack today and I don't know where I was. Tom, what am I going to do? I think I'm going mad... I think I'm the one attacking everyone, Tom!""
 * At one point in Darkly Dreaming Dexter, Dexter suspects that he may be the Tamiami Butcher. This turns out not to be true, but is justified at the time given the bizarre dreams he has and the fact that he is a serial killer.
 * The Stephen King short story "Strawberry Spring," which appeared in the collection Night Shift.
 * Also the novella "Secret Window, Secret Garden," and later the Johnny Depp film adaptation.
 * Interestingly, the Jim Thompson novel The Killer Inside Me isn't an example of this trope, as it's told from the first-person perspective of a character who knowingly and admittedly is committing the murders in the story, and isn't hallucinating or hiding anything.
 * Thompson likes this trope a lot. Inverted in Of course, this probably wasn't the original ending he had in mind.
 * in The Scent of the Night- throughout the book everyone is looking for Gargano, who stole a lot of money from some very angry people.
 * Michael Crichton's novel Sphere used a similar twist.
 * If Harry Potter and the Chamber of Secrets were told from Ginny's POV (and it has been several times if you count fan fiction), it would fit this pretty well:
 * If Harry Potter and the Chamber of Secrets were told from Ginny's POV (and it has been several times if you count fan fiction), it would fit this pretty well:


 * At least, sort of; she's actually being possessed by.
 * The Erast Fandorin story Leviathan features an English aristocrat who accidentally killed his wife through dangerous driving, went insane as a result and has internalised the story: he recounts it as though it happened to someone else and turns violent when confronted with the truth. This isn't a major part of the story and is not a revelation to the other characters, but is to the reader.
 * Oedipus Rex is a classic example of this trope.
 * At the end of 'Monster' by Diana Hoh, the protagonist disovers that she is in fact the monster who has been attacking her fellow students, due to a science experiment that went wrong, causing her to transform into a monster and have no recollection of the attacks. A very surprising twist, as she never even suspected herself. Also a theme in another of Diane Hoh's books, 'The Night Walker,' in which Quinn suspects that she is attacking people while sleepwalking.

Live-Action TV

 * Ironically, the Buffy the Vampire Slayer episode "The Killer in Me" is not an example of this trope. The earlier episode "Sleeper" however has Spike as a Manchurian Agent under the control of the First, killing and then having no memory of having done so.
 * The Angel episode "Somnambulist" at first appears to be an example of this trope, but it turns out that Angel is having dreams as a result of his connection to one of his vampire progeny, who is the actual murderer. This does make Angel indirectly responsible.
 * Davis of Smallville, who turns out to be the human form of General Zod's pet project,.
 * One murderer in Criminal Minds didn't seem to realize he was a killer until the BAU themselves showed him proof. In this case, though, it's made abundantly clear to the viewers that he's the killer from very early on, so it's only a shock to him. This leads a rather bizarre and intense interrogation scene where the BAU keep showing him more and more evidence that he did it and he keeps refusing to believe it...until it all comes back to him.
 * In the Beyond Belief: Fact or Fiction? segment "Malibu Cop," the titular detective discovers that he himself is the murderer he is searching for. He committed the crime while sleepwalking. Supposedly this story was "Fact."
 * Subverted in an episode of Law and Order where a sleepwalking cop (who has a rather mean personality while doing so) is the suspect, but it's quickly established that he wouldn't have been able to commit the murders since his sleepwalking self couldn't use a gun.
 * In season 6 of Dexter
 * The TV movie In The Shadow Of Evil is about a cop who develops amnesia while on the case of a serial killer whose pattern indicates he will kill again in a month. Towards the end of the month he has regained enough of his memory to realise he's investigating himself and switches from Type B to Type A.

Music

 * Krayzie Bone's song Don't Know Why. Krayzie essentially blanks out after killing his ex employer but don't remember doing it. He wakes up in a grave yard covered in blood. Of course It Got Worse for him when cops show up at his front door more or less confirming his fear..

Theatre

 * Arnold Schoenberg's song-cycle/single-role opera Erwartung (Expectation) -- In a forest, an amnesic woman looks desperately for her lover. She finds his bloodied body and cries out for help. Her memory gradually falls into place—she has killed the man for his infidelity.
 * Sort of : Part of one of the oldest known Twist Ending : In Oedipus Rex, the main character spend the play trying to find the murderer of the previous king. At the end, somebody make him realize he (unknowingly) killed him. It only goes down from there...

Video Games

 * The Suffering: Ties that Bind: At the end of the game, it is revealed that Blackmore is really Torque's alter-ego.
 * In Max Payne 2 The Fall of Max Payne, the show within a game Address Unknown ends like this: The protagonist, who spent the entire show looking for the murderer of his family, a man named John Mirra, realizes that he was the killer after he sees the killer's face staring back at him in a bathroom mirror. This, incidentally, may mean the whole purpose of the show was to set up a truly terrible pun: he solves the mystery in the bathroom (as in, the john) by looking into the mirror... Also a Tomato in the Mirror.
 * In Xenogears when we find out that is really another personality of.
 * Inverted in Tsukihime, where Shiki sees himself walking around the city at night and killing people when he should be sleeping, and fears that this trope is in affect. Actually, Although he really DOES have a killing impulse and a killer in him, but it only targets non-humans.
 * In the Chzo Mythos,  This is referenced in the special edition commentary, though never clarified.
 * In Silent Hill 2,
 * Part of the backstory of Siegfried in the Soul Series. He swears to avenge his father's murder. Guess who did it..
 * Heavy Rain sets this up fairly early on with Ethan Mars, who has periods where he blacks out then wakes up with an origami figure in his hand.
 * In Twisted Metal: Black, Preacher believes that he is the victim of Demonic Possession after an exorcism, with the "demon" driving him to kill.
 * A fairly common type of bugs in RPG with Procedural Generation is missing sanity checks on most generated content. Among the other things, it allows NPCs to choose their allies and even themselves when they decide to act against a random available NPC or offer others a quest to do so. This tend to mix badly with Relationship Values and faction helping its own members, of course.
 * The most famous is Crusader Kings II bug making characters try to capture or assassinate themselves, and then report themselves for this. The most famous one (thanks to Reddit) is Spymaster Roger a Muirebe reporting himself for trying to assassinate himself so that he won't discover his plot to kill himself (see on Reddit, me.me).
 * Dwarf Fortress changelist in 2008 included «Stopped people from giving quests to kill themselves.»

Western Animation

 * Patrick Star of SpongeBob SquarePants parodies this. He was trying to find who made a clam cry, and finally found it was...himself. Complete with, "It's the perfect crime!" Spongebob did it, though.
 * Except he didn't. It Makes Sense in Context.
 * Also parodied in the episode where Spongebob becomes a hall monitor: he begins hunting down a maniac that has been terrorizing the town, unaware that the "maniac" actually refers to him doing his antics of the episode. Leads to a bizarre scene where Patrick is using a walky-talky to report on the maniac's occasion and somehow, Spongebob just can't run away from him!