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It's the perfect locked-room mystery: the police find the victim murdered, but the room is locked from the inside. How did the killer escape? He didn't. After committing the murder, the killer committed suicide and then destroyed his body, leaving no traces.

How can a person destroy their body so that no traces of it are visible?

To clarify, the traces of the person's body do not have to be completely undetectable, but a non-expert should not be able to find anything suggesting a corpse (i.e. Sherlock Holmes could deduce that the killer had destroyed himself, but Inspector Lestrade wouldn't be able to work it out).

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closed as off-topic by Ryan_L, Trish, Arkenstein XII, G0BLiN, Ash Jul 22 at 12:36

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about worldbuilding, within the scope defined in the help center." – Trish, G0BLiN, Ash
If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ We need to know what the locked room is. Is it the lion's cage at the zoo? A factory with molten metal (a la Terminator 2)? A crematorium? A greenhouse? A sausage factory? The piranha exhibit at an aquarium? It's going to be a lot more difficult if it's just a regular room where the killer has to bring the means of destroying the body. $\endgroup$ – Brythan Jul 21 at 20:27
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    $\begingroup$ Unsolved mysteries are interesting to readers. Wierd, complex, but solvable mysteries are interesting to readers. Utterly unsolvable mysteries are tedious and dull to readers. If insanity, leprechauns, and aliens are equally plausible alternatives to explain the murder-suicide mystery, then you have probably lost the reader. $\endgroup$ – user535733 Jul 21 at 21:53
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    $\begingroup$ An obvious flaw in this is why the murderer did not simply destroy the victim's body leaving no trace ? Once there is any means to work out two people went in and just one came out either this or the OP's scenario makes discovery of a murder very likely. In the absence of proof that two went in and one came out, then the murderer can get away with walking out alive and need not commit suicide. $\endgroup$ – StephenG Jul 21 at 22:01
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    $\begingroup$ @StephenG I don't really have a good response to that, but if you're the sort of murderer who is willing to commit suicide in order to elaborately cover up your crime, you are doing it intentionally to bamboozle the police for fun, rather than actually trying to hide the body in the most effective way. $\endgroup$ – mprogrammer Jul 21 at 23:56
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    $\begingroup$ We would seem to have very different defintions of "fun" if "you are doing it intentionally to bamboozle the police for fun" includes suicide. $\endgroup$ – JRE Jul 22 at 12:04
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If the locked room is a morgue, then the murderer poisons his own twin brother and makes sure the body is checked into the morgue. Before the autopsy, he lures the victim there, murders him, burns his twin brother's body in the medical incinerator, burns all of his own clothes, rearranges all the bodies in the morgue (just to mess with investigators), and then lying in a morgue refrigerator crisper bin or whatever they are called, swallows the poison he used to poison his twin brother.

Oh, and he hasn't eaten anything for 48 hours, and gave himself an enema, and peed before laying in the cold metal thingy they keep bodies in so he doesn't crap and piss himself when he dies.

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    $\begingroup$ What an awesome last day checklist! Well done! $\endgroup$ – user535733 Jul 21 at 21:58
  • $\begingroup$ why does he need a twin why not just put himself in the incinerator $\endgroup$ – sdrawkcabdear Jul 22 at 17:04
  • $\begingroup$ Because bones need to be ground up after a body is cremated. They get chunky and charred and are not gasified in crematoria. That would leave a telltale clue as what happened to the murder. $\endgroup$ – EDL Jul 22 at 20:35
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How much time is allowed before discovery?

The room has a sink made of a material that can take a good amount of heat. Stainless steel comes to mind but there very well might be other materials that aren't coming to mind at the moment.

After doing his dirty deed the killer climbs onto a contraption sitting in the sink. (This will be a bit precarious due to the narrow base it must have. There could be additional supports while he was getting in that are then removed.) He's lying on a membrane separating himself from a mixture of sulfuric acid and hydrogen peroxide. After he's dead a timer triggers, making a hole. In time the chemicals dissolve the body. (Yes, this is basically a scene from Breaking Bad. The show didn't give the details and it wouldn't have worked exactly as shown anyway.)

After enough time has elapsed a second timer opens a drain line which is run down the drain past the metal parts. Away goes your chemicals and all obvious traces of the body. Removing all that weight causes the device to fold up (and pulls up the drain line) and triggers the next stage--the release of a solvent for the plastic of the main part of the machine. The last piece to melt through is another drain--that part is now gone.

Yet more time, a container of water ruptures, washing the gunk out of the trap. At this point you have some scaffolding, the bowl that held the melting plastic and whatever held the water. (The timers are chemical in nature, no electronics are involved.) These are all built out of something that will burn slowly and cleanly, the last stage is to burn it. (This timer might be as simple as something that will spontaneously ignite once dry--but it was in the water holder.)

There's no such thing as truly zero residue from burning a solid, there will be traces left but not much. A disguise of a controlled kitchen fire earlier would make it even harder to find. (Something on the stove burnt in a situation that kept the size of the fire down. Lots of smoke but no fire damage. Leave the burnt stuff as evidence of the nature of the fire.)

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Thermite

The murderer could use thermite to dispose of their own body (could be a timer-based device that ignites it) or simply to commit suicide (but that would probably be rather painful). The only problem is that it burns slightly hot and could potentially just incinerate the whole room so a lot would depend on the environment - ceramic tiles in morgue would probably be fine, some old wooden shack would probably burn down.

Since there will be a lot of ash, the murderer could make it look like hiding the evidence even further - throw some clothes, computers and other stuff to the burning pile and the body might not be detected so easily.

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    $\begingroup$ Thermite would also leave a lot of molten metal, and typically this would have slag on the top due to impurities – the ash would likely be hidden in the slag, and only really detectable if someone analysed the slag and knew the original composition of the impurities so could detect the extras from the body. However, unless there was an explanation for the thermite residue, someone might easily guess that a body had been burnt. $\endgroup$ – Dan W Jul 22 at 12:07
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Human Candle/Wick Effect

https://en.wikipedia.org/wiki/Wick_effect

If a sufficiently rotund body is wrapped in wicking material, and then set alight. The body can be almost completely destroyed/cremated owing to the makeshift reverse candle that is created.

The body slowly imparts oil to the wick/clothing. This slow burns creating intense temperatures, which destroys the body.

Typically in this process, the legs are usually left intact.

To counter this, our "hero" could cover his feet in lard before rolling himself up in a carpet, and setting himself alight.

As a bonus, this process in the wild, typically does much less damage around the body than would be expected.

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Acid in a barrel, connected to a drain pipe, with a timer to open a drain valve (and some neutralizing alkalic solution). But watch the mythbusters episode about Breaking Bad.

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  • $\begingroup$ You mean the one where they dissolved a pig carcas in piranha solution? If there is anything to take away from that episode, then that this method of body disposal is anything but discreet due to the huge amounts of toxic smoke and fire it creates. Just cremating a body the regular way creates far less of a fuss. $\endgroup$ – Philipp Jul 22 at 10:57
  • $\begingroup$ @Philipp: ok, you need a secon timer, a cirucaliton pump, and a cover. updating my answer $\endgroup$ – Sascha Jul 22 at 11:25
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Another and less usual way to destroy a body is by decompression. If you've got a good stomach for gore, google for some decompression accidents.

I believe it's possible to more or less liquify a body, so it could be drained away.

I can't find a citation for that right now (thought it was the Byford Dolphin, but not sure), and don't feel like reading reports on it again... someone else can, ah, flesh out this answer...

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