One of the popular plots in detective stories is the investigation of a murder which has been—so far—successfully disguised as a suicide. It’s a popular plot for a reason, offering some very interesting possibilities for stories. It does, however, come with some requirements on the stories containing it, which I’d like to discuss.

The first and most obvious requirement which faux-suicide poses is that of means. People tend to kill themselves in one of a limited number of ways, and in any event must kill themselves in a way that is plausible to do alone. A man cannot shoot himself in the back with a rifle from a great distance. Further complicating the faux suicide, the murder weapon must be plausibly accessible to the victim when the body is found. Dead men do not move murder weapons. The murderer must then have access to the body after the murder in order to plant the murder weapon in some fashion. This precludes, or at least makes very difficult, the locked room murder.

Of course, that’s really just a challenge to the writer, and there have been some clever solutions. I think my favorite is a room that had both a deadbolt and a latch; the murderer locked the dead bolt but left the latch unlocked then broke the door open, staged the suicide, then locked the latch. When the detectives broke in, they assumed that the deadbolt was broken then, and not already broken. That was quite clever. (This is the Death In Paradise episode at a nursing home.)

The limitations on the means of suicide are more strict, though. For example, any poisons used must be very fast acting. Poisons like arsenic which cause pain for days before death finally comes are simply not plausible as a means of suicide. Elaborate traps which catch the victim by surprise are also implausible. Simple drowning is right out.

Additionally, the means of murder have to be something one can force on a person without leaving bruising that will contradict the idea of suicide. It will not work to knock a man unconscious with a frying pan before staging his suicide with a gun. Sedatives are the easy way out, but they’re a gamble because a toxicology report will then prove that it was not murder. Another alternative is providing an explanation for bruising will also work, such as pre-mortem bruising, faking the victim changing his mind at the last minute, or damaging the body post-mortem such as by throwing it off of a cliff.

The second sort of requirement which faux-suicide imposes is on the conditions of the victim, pre-mortem. The victim must have some sort of plausible reason to have killed himself. This significantly limits the sort of victims one can have. It would be very difficult to disguise the murder of a successful man in good health as suicide, for example. It’s not impossible, of course, but the attempt will tend to involve faking a scandal which would ruin the man’s life. It’s doable—it’s certainly doable—it just introduces other problems which need to be solved in order to make it work.

The final requirement imposed by a faux-suicide is about the detective: why on earth is he investigating the crime? If it’s suicide, what is there to investigate? The perpetrator of the crime is already known.

Proximally, there’s only one reason: because someone thinks that the faux suicide was not suicide. In a sense this is just a sub-case of the more general case of there being someone who is widely accepted as guilty, but there is someone who does not accept their guilt. In both cases, there can even be a confession (a suicide note, in the case of the faux suicide). That said, I think that there are enough differences to consider the faux-suicide on its own, rather than just as a special case of the more general pattern.

The reasons for the detective investigating the faux-suicide seem to me to come in roughly two main classes:

1. Some of the facts of the scene of the crime are inconsistent with the suicide theory.
2. Someone who knows the victim does not believe they could have killed themselves.

There is a very good example of #1 in Death in Paradise. Detective Richard Poole does not believe that a woman could have killed herself because she had only drank half of her cup of extremely expensive tea. (He also thinks it unlikely she could have drowned herself by sheer force of will, and she drowned but had no bruising anywhere on her, nor any sedatives in her system.)

Another example of this is the death of Paul Alexis in Have His Carcass. His blood being liquid and there being only one set of footprints—his—up to the flatiron rock suggest suicide, but on the other hand it seems implausible for a man with a full beard to buy a cutthroat razor, then take a train (with a return ticket) and walk 5 miles to sit on a hot rock for several hours before cutting his own throat with the razor.

Have His Carcass also gives an example of the latter category—a wealthy widow who was engaged to Paul Alexis thinks it is impossible that he killed himself and begs Harriet Vane to find out who murdered her intended husband.

The first category is, I think, far more common than the second sort. I can’t, off hand, think of any examples in which a detective investigated a murder solely on the strength of someone thinking it impossible their friend committed suicide. The closest I can come to that may be Five Little Pigs, in which Poirot investigates an old murder because the convicted woman’s daughter is certain her mother is innocent. Her certainty comes from a letter from her mother assuring her daughter she is innocent. This, and that her mother always told the truth. In that story, though, Poirot did not accept the mother’s innocence and was explicit that he would tell her if his investigation made him think the mother did it.

It seems, then, that a faux suicide usually requires some amount of inconsistent facts in order to be a viable story. The question then becomes how to balance these facts such that the detective understands their meaning but the authorities do not. In a sense, this is just a sub-class of the problem of how to give clues the detective understands but others don’t; still, again, I think that it is worth looking into the specific case.

I think that, as a rule, the evidence in favor of suicide should be the main physical evidence, while the evidence against should be the more subtle psychological evidence. This is certainly the common pattern, at least, but I think it makes sense since small psychological inconsistencies are easier to brush away as explained by information not present. People occasionally do strange things, and suicide is almost definitionally the strangest. No one kills himself more than once in his life.

But, then, why does the detective—who knows better than anyone that life is sometimes just unaccountably strange—place such high value on the evidence which others dismiss?

One common answer is that the detective has a compulsion to make sure that everything is neat and orderly and makes sense and is explained. This is not very satisfying, though, since this trait must be selectively applied as life is very rarely neat and orderly, with everything having an explanation which makes sense.

Another approach, which is better but still not great, is that the detective has a hunch. It’s not really satisfying because it violates rule #6:

No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right.

That said, this is a fuzzy line. One man’s unaccountable hunch which proves right is another man’s feeling that he can’t articulate but bears further examination.

One variation of this which is not so much a hunch is giving the detective highly domain specific knowledge. “No deep sea diver would ever drink tea at this time of day”—that sort of thing. The problem is that unless one can prevent the authorities checking up on this, they will be immediately forced to conclude the suicide was not suicide. (This is sometimes dealt with by making the authorities very pig-headed or otherwise very budget-constrained, so that they will jump at the chance to classify every death as a suicide so as to avoid having to investigate it. It an be pulled off, of course.)

I think what probably works out the best is inconclusive evidence that the suicide is fake combined with someone other than the detective acting as the driving force. The detective may not have unaccountable hunches, but others may. This sets up the interplay that the other person is sure that it wasn’t suicide, while the detective can only see some evidence which supports this conclusion but at least does justify further investigation. By making the motive force a hunch, there does not need to be sufficient evidence to justify the hunch. This allows the faux suicide to be generally taken as suicide without all of the people involved being dimwits. Unless the murder mystery is also a comedy, it is preferable to populate the world with reasonably intelligent people.