I'm toying with a scenario however it's crucial to the plot that the murder doesn't know they're guilty and has to work with their friends to try and solve the murder.

This is probably set in the real world, maybe historical possibly fantasy but I'd rather keep this element as real world as possible.

I've thought about drugging, the "criminal" being blind drunk or taking a whack to the head but it strikes me all of these would leave some sort of evidence which could tip off the guilty party (hangovers/injuries). I'm really hoping to build that "Oh - it's me!" moment.

How can I arrange a murder without tipping off the murder that they are the criminal?

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    I am worried this is too broad/off topic - let me know if it is and I'll delete it. Still hoping for some good ideas, my best so far is "They're a werewolf and don't know it..."
    – Liath
    Commented Aug 5, 2014 at 8:55
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    @JMK I was thinking more like Poirot discovering he was the murderer!
    – Liath
    Commented Aug 5, 2014 at 11:55
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    Try giving him too much Xanax. It will give them amnesia really bad. He would only remember a couple things if anything at all and what he did remember would seem like a dream and not real. Throw in some alcohol and make him wake in a pool of blood. Oh god -shutters. Example, browse the forums you will see Xanax is no joke. drugs-forum.com/forum/showthread.php?t=7945
    – Tony
    Commented Aug 5, 2014 at 18:41
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    NOTE TO EVERYONE WHO WANTS TO BE HELPFUL: Accidentally killing someone, or inadvertently causing someone to die (especially through inaction!) is NOT murder.
    – dmm
    Commented Aug 5, 2014 at 20:48
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    Perhaps not a good fit for the kind of story you want, but the first thing that popped into my mind when I saw the title was that the crime simply didn't register as extraordinary to the criminal. "For me, it was Tuesday." Commented Aug 6, 2014 at 2:52

16 Answers 16


I suggest you search Google Scholar for scientific publications on the matter. For example, Porter, Birt, Yuille and Hervé (2001) list several publications that report real cases of perpetrators forgetting that they committed homicide or other extreme violence. This is the abstact for that paper:

Mental health professionals and legal decision-makers often hear reports of memory impairment from both perpetrators of extreme violence such as homicide (e.g., Kopelman, 1995; Roesch & Golding, 1986; Schacter, 1986a), and from complainants and eyewitnesses (e.g., Loftus, 1993). Adult complainants, for example, have testified about their recovery of repressed memories for a violent incident(s) following a lengthy period of amnesia (e.g., Loftus, 1997; Porter, Yuille, & Lehman, 1999). Although these two types of cases differ in the timing of the memory loss (current vs. historical), both require a consideration of the validity of dissociative amnesia. Dissociative amnesia refers to amnesia for a traumatic (and, in this context, criminal) experience which has a psychological origin. Whereas dissociative amnesia refers to a process of forgetting following a traumatic experience, a dissociative state refers to an altered state of consciousness occurring during a traumatic experience. Dissociation is the more general term referring to the separation of any normally integrated psychological processes, encompassing both dissociative amnesia and the dissociative state.

I'm sure there is more than that, this was on the first page of search results.



Off the top of my head, solmnambulation and memory-impairing drugs are probably the easiest and most probable. Human memory is somewhat frail. In real life this generally impacts the accuracy and availability of memories, but yes, under the right circumstances people can fail to remember having done something. Many things affect memory, and with a little research I'm certain you could find at least ten scenarios that I'm not even thinking of right now.

I am working off of the assumption that you're not interested in trauma-related memory suppression.

1) Sleep-walking is not uncommon, and people who sleep-walk are able to perform all sorts of complex actions while immersed in slow-wave sleep. Look up homicidal sleepwalking on Wikipedia, it's a hoot. As a bonus some medications can cause sleep-walking as a side-effect, including a certain popular insomnia aid.

2) Certain drugs can cause memory loss or poor memory formation. One such is GHB which has gained some notoriety for its use in date rape. It's also occassionally found to have been used in cases of mugging and the like, and it can be difficult to detect. There are certainly other drugs that affect memory, too.

3) Just in case, there is always the possibility of post-traumatic memory loss. In fiction (especially movies) one commonly finds this trope in conjunction with hypnosis. Memory repression hearkens back to Freudian psychoanalysis. This choice has a strong whiff of pop-psychology, and hypnosis therapy in particular is highly controversial.

Hopefully these options can give you something to chew on.

  • While people usually don't remember what they did when they sleepwalked, I have never heard of anyone commiting a murder in that state. Liath should research this before they use it.
    – user5645
    Commented Aug 5, 2014 at 13:00
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    @what I have heard of sleep-eating and even sleep-sex. I suppose it's possible for someone into rough sex to have really rough sleep sex and kill the person, but you'd have a naked corpse in your bed and evidence of sex on you, so unless you sleep-shower and sleep-cover-up-evidence too... Commented Aug 5, 2014 at 13:03
  • @LaurenIpsum At least sleepwalking as been used as a defense in homicide cases. Cf. scholar.google.com/scholar?q=sleepwalk+murder I haven't read any of the papers, so I I don't know if the defense of murder while sleepwalking held under psychological scrutiny.
    – user5645
    Commented Aug 5, 2014 at 13:15
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    – lea
    Commented Aug 5, 2014 at 13:55
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    Whether anyone really has committed a murder while sleep-walking, the idea doesn't seem obviously, blatantly impossible. By definition, fiction is not limited to things that you can prove really happened -- that's called "non-fiction". I'm pretty sure that no one has ever actually travelled to the planet Vulcan or survived a total nuclear war, but that doesn't mean you can't include such things in a fiction story.
    – Jay
    Commented Aug 5, 2014 at 15:07

Is your story based in the present day?

You mentioned Poirot which is of course based during WWII.

If your story based in the past as well, you could maybe work medicine into this, specifically medical practices which used to be valid and have since been discredited as harmful.

Maybe your character thinks they are helping the victim by providing a certain medical treatment, the victim dies, the coroner asserts that they have been poisoned, and then the main character sets out to track down the perpetrator, only to find out it was them?


Some bacterial/viral diseases have been known to affect the formation of new memories (see the famous case study of Clive Wearing).

Perhaps a character is yet unaware of their diagnosis, and things in their life start "slipping through the cracks".

Lack of attention promptly after an event can also interfere with the formation of memory. Perhaps something startling happens to the character exactly after or even during the fatal event. This is a little far-fetched unless the killing itself is somewhat accidental or even incidental, as such a powerful emotion (associated with committing a major crime) would dominate one's attention. But for example, someone could "bump" something on the road, be concerned about it, but before checking up on the matter receive a phone call from one's mum. Two weeks later the character hears about a hit and run and finally realizes it was that fateful bump. Quite a moral dilemma here whether or not to turn oneself in. Perhaps the character calls back her mum to see if she remembers anything notable from the time of that call--looking for clues/salvation/deniability. What a taught conversation that would be. hth.


I might suggest the idea of fugue states. While more commonly caused by drug or alcohol abuse, they can also be caused by epileptic seizures.

My father experienced Grand mal seizures and if he had a seizure while no one else was around, was sometimes found later with no memory of the seizure or the time before or after it. Later in life, when he was on a number of heavy medications to address them, he specifically began doing (or attempting to) dangerous things directly after a seizure (like standing in front of an oncoming train believing that he was impervious). He had no conscious memories of any of his activities or even his seizure.

  • Plot of Angel Heart, he was effectively reborn when he sold his soul


  • He commits the murder by accident, e.g. he wonders what a switch does, flicks it nothing happens. That causes someone to be electrocuted outside (but with a few layers of indirection)

  • Time travel, he hasn't killed him yet

  • Something dangerous laying around that without thinking he tells a child to just get rid of, that child posts it through the neighbours letter box, e.g. peanut butter, allergic reaction follows

  • Similar where he tells someone to 'just take care of it', later he finds that the person took care of it by cutting power to a building, the building hosts life support (e.g. a criminal will leave a building so cutting power stops the lifts, he's lazy so won't go out)



You say that making the character drunk wouldn't work because there'd be evidence, e.g. a hangover. But so what? If someone woke up with a hangover, he'd know he'd been drunk, maybe he'd realize that he didn't remember anything he did the night before, but it would be quite a leap from "I was so drunk I don't remember what I did last night" to "I must have murdered someone".

Ditto various other drugs.

The idea of a brilliant detective being a drunkard or a drug addict seems a little out of character to me, but you could always come up with a reason why this one time he did something out of character, like an extreme personal problem. Or someone deliberately drugged him. (Ooh, suddenly gave me an amusing idea: A woman wakes up to realize that someone has given her a date-rape drug. While she's trying to figure out just who did it and what he did to her, she finds out that while she was drugged, she murdered someone. Like, she's thinking she was the victim and then it turns out she was the criminal.)

People who have amnesia don't remember what they did. That's pretty much the definition of amnesia. You'd have to give some explanation for it -- you can't just say, "oh, by the way, he had amnesia".

If it's a science fiction story, you can always invent some machine that erases memories. Then you can introduce the machine early in the story and have it be a part of the plot way before you reveal that it was used on the detective.

To follow up on someone else's suggestion: Is it necessary to your story for the hero to have deliberately killed the person? If not, then it could be some sort of accident and he doesn't realize anyone was killed. Ranging from "I wonder what this switch does?" to "I thought I hit someone with my car in the dark but there's no sign of a body", like because the person was thrown somewhere that the hero can't see the body, or maybe he runs away and dies somewhere else.

BTW saying this or that scenario would leave evidence: That would be a good thing, so there is some foreshadowing. You don't want to get to the final scene in the story and then with absolutely no warning say, "And then he noticed that the glove found at the scene was a perfect match for the one glove in his own coat pocket. He suddenly realized that he himself was the murderer. The end." There have to be some clues building up to this point. An early scene where the detective has a period of time that he doesn't remember what he did, which is then explained away in some plausible manner, and then brought back at the end, if done properly could be a nice piece of foreshadowing.

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    "The idea of a brilliant detective being a drunkard or a drug addict seems a little out of character to me." Read any Sherlock Holmes stories lately? Commented Aug 5, 2014 at 16:04
  • Sure. And I thought it seemed out of character. Of course Holmes was supposed to be .. quirky.
    – Jay
    Commented Aug 5, 2014 at 18:12
  • Then you didn't understand how his mind worked. He constantly needed input, data, intellectual stimulation. If he couldn't get it from a puzzle/crime, he turned to drugs. It's an integral part of the character in any incarnation. Commented Aug 5, 2014 at 19:57
  • (Shrug) Not a question that will lead me to challenge you to a duel to the death. It seems to me that a brilliant detective would value his mind highly, and would want to keep it clear and functioning at peak efficiency. Hallucinogenic drugs would seem like the sort of thing a brilliant detective would have no desire to use. I suppose you could make a case that "a mind forever wandering" would try such drugs out of curiosity, but that's not how I recall it presented in the stories. Of course one must also consider that cocaine and heroin use were viewed differently back then. Whatever.
    – Jay
    Commented Aug 5, 2014 at 20:58
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    You make exactly the case that Watson did, and the good doctor weaned Holmes off the 7% solution after a few years as a fellow lodger. BBC's Sherlock is clean when John meets him (but admits using in the past), and JLMiller's Holmes on Elementary goes to 12-step meetings regularly as part of the show. Commented Aug 5, 2014 at 21:54

Let your character be a greedy, busy bounty hunter. He does everything as long as it is well paid. Murder, surveillance, investigation. All for money. He does not really cares about who he kills and who he helps.

The guy deserves to end up inquiring into one of his own old murdering contracts!


Sleepwalking, as many have mentioned, is one way to pull this off. I also don't see why a night of heavy drinking is out of the question. So they woke up with a heavy hangover and their shoes missing (or something) one morning--so what? Especially if the character has a history of heavy drinking, this won't seem out of the ordinary.

But there's another option: what if they do remember everything about the crime, but don't realize its significance until later? In other words, the murder was a complete accident. Perhaps the victim died in a fire, and your character only realizes much later that the fire was started by a cigarette they forgot to put out. Like any detective story, the chain of events here can be as simple or as complex as you like, and it could give you plenty of opportunities to throw out hints and red herrings along the way. Plus, it requires no supernatural elements, drugs, amnesia, sleepwalking, split personalities, or other unusual elements--just simple carelessness or ignorance.


“If once a man indulges himself in murder, very soon he comes to think little of robbing; and from robbing he comes next to drinking and Sabbath-breaking, and from that to incivility and procrastination. Once begun upon this downward path, you never know where you are to stop. Many a man has dated his ruin from some murder or other that perhaps he thought little of at the time.” ― Thomas de Quincey

There was a book--the title and author of which I have utterly forgotten--where a ferry captain is involved in smuggling; he is bribed to contrive to bring a van aboard the ship without its going through Customs. Halfway through the voyage (from the Netherlands to the UK, I think), he becomes convinced that the police at the destination have been tipped off. Panicked, he stages a bomb-threat and has his crew push the van off the ship into the North Sea.

Later, he learns that the van's cargo was illegal aliens.

Would something like that do? The person is convinced to commit a crime, but one that he does not realize will lead to a death (a burglary of vital medication or medical equipment perhaps?) At some point, he discovers the connection, which he cannot expose without condemning himself as an accomplice and co-conspirator.


I believe this is part of the plot of the movie (spoiler below)


although I'm going on the Wikipedia summary, as I've never seen it.

I've read at least one sci-fi short story (dystopian future) where criminals went to a black market memory wiper and had their memories erased. The criminal became a different person; that "person" isn't the one who committed the crime.

So I suppose the post-wiped person could become a detective who specializes in cold cases, and she eventually comes across a murder which is starting to sound naggingly familiar but she can't put her finger on why...


Going at a slight tangent, Derren Brown once convinces a man that he committed a murder (which he did not), and forgot about it.

The episode is called "The Guilt Trip" from the series "The Experiments".

He does this through conditioning and triggers to invoke a feeling of guilt. Everyone around him are actors and he uses them to start messing with his memory and make him doubt his own mind. Getting actors to change clothes when he's not looking, swapping food plates...etc

He sets up a motive and then uses a drunken night and the triggers to convince him of the murder.


Protein synthesis is required for memory consolidation, so you can use protein synthesis inhibitor to block formation of long term memories in theory. See Gold. Protein synthesis inhibition and memory: formation vs amnesia (2008) for example.


Total Recall They simply have a machine that does "memory implants" and "memory wipes." Based on Philip K. Dick's short story "We Can Remember It for You Wholesale."

Slight spoiler, mostly from Wikipedia:

Douglas Quaid is a construction worker who discovers that he is actually a secret agent formerly named Carl Hauser. He travels to Mars to uncover his true identity and why his memory was erased. Adventures ensue.

Worse spoiler, from me:

In the end, you are left wondering which person really exists. Is the spy Hauser only a figment of Quaid's imagination, and everything that seemed to have happened on Mars only the result of a malfunctioning "vacation machine," exactly like his wife and friends were telling him at the beginning? Did Quaid reject his mundane real-life for a much more interesting dream-life? And if so, is he really worse off? Or, was part of the Mars adventure real, but the spy Hauser was only a memory implanted by the bad guy into Quaid, to use Quaid to ferret out the resistance, as the bad guy mockingly tells Quaid 3/4 into the movie? Or, is Quaid real, and Hauser was an implanted persona to neutralize Quaid without killing him?

  • I don't know if your "worse spoiler" is a spoiler at all (and not only because it is from a 24-year-old movie). Your speculation is a popular theory, but there is almost no support for it in the movie, except the way the plot tracks the protagonist's wishes, and given that his wishes are a more-exciting job and a girlfriend with big breasts, that isn't some huge coincidence. Commented Aug 6, 2014 at 0:06
  • Well, who wouldn't want those things??? Someone can change "you are" to "I was" if they want. I put the speculation in there because it was pertinent to the question.
    – dmm
    Commented Aug 6, 2014 at 0:48

2 ideas:

  1. There was a planed murder (poison/trap/bomb) and the Character interupted the plan... and unknowingly triggered the Dead condition .. prepared by somebody else.
    • taking poisoned drink to some one else..
    • detonated a bomb with a phone call..
    • dropped a banana .. and 2 minutes after, someone behind him broke his neck...
      Just work out a nice chain of events.

2.This is bit cooler: Commiting a crime by NOT acting.
- a friend calls "It is urgent please tell me...", "sorry dude no time for this now I'm at work". Two days later you get the news your friend is dead ...
- "Son please go to see the old lady next door, she asked for some help".

  • The criminal law is against you: there is no such thing as a crime of inaction. A crime requires an act. The only exception I can think of is a narcotics conspiracy which, unlike other conspiracies, does not require an overt act. In a conspiracy, the words of agreement coupled with the commission of a criminal act by a co-conspirator were enough to impose liability on all of the conspirators. But thankfully, we do not have thoughtcrime...at least not yet.
    – user26732
    Commented Aug 12, 2014 at 19:39
  • The criminal law I am referring to is U.S. federal criminal law and U.S. common law. Otherwise, YMMV.
    – user26732
    Commented Aug 12, 2014 at 19:40

I have seen a similar scenario on the TV show House MD which goes like the following:

A person sets up a situation where they bring the target into a situation that seems safe, however their unconscious adds in an element that they "want", and turns out to be dangerous for the target, that in hindsight the person knew it was dangerous, but not at the time they made the decision - it simply wasn't on their mind.

  • To be fair, that describes quite a few episodes of House. Were you referencing "Safe"? imdb.com/title/tt0774238/?ref_=nm_flmg_act_26 Commented Aug 5, 2014 at 16:06
  • The specific episode I had in mind was Chase's bachelor party, but as you said, quite a few episodes can have such a situation Commented Aug 5, 2014 at 16:09
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    Oh yeah, I managed to forget that whole plot arc of House losing his mind due to Vicodin abuse (which was inserted at network insistence, BTW; that drug doesn't have that side effect). Commented Aug 5, 2014 at 17:10
  • The final episodes of FX's (now Netflix's) The Killing deals with this theme. Someone suggested sleepwalking as a solution. Take a look at the literature on Ambien Zombies. There are dozens of cases of prosecuted Ambien Zombie crimes where the perp has no recollection whatsoever of his acts.
    – user26732
    Commented Aug 12, 2014 at 19:35

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