I’ve written before about how murder mysteries with a clever twist are less popular than they were during the golden age (see Ingenious Murders, Alibi By Recording, and Dorothy L. Sayers and Clever Murders.) There is a variant of the clever twist which I would like to consider more specifically: the trap. For the purposes of this blog post, I’ll consider traps any method of murder where the murderer does not need to be (immediately) present at the time of the murder.

The first thing to get out of the way is that there is one kind of trap which remains as popular as ever: poison. We don’t tend to think of poison as a trap because it doesn’t have any mechanical parts but it functions exactly in the same manner as a shotgun in a closet whose trigger was on a string to the door. It’s just smaller and you have to trick the victim into eating it, which is rarely necessary with a shotgun.

The main problem that traps have, from the perspective of the murderer, is that they make most alibis useless. Unless the time the trap was set up is very tightly constrained, it requires a very long alibi to ensure one could not have set it up. It’s difficult to both be a character in the story and to have an alibi for several days straight. (People can, of course, lie about when they arrived in the country, but it’s too easy to check the dates on their passport.)

There is a solution to this, though, which is to disguise the trap so that it appears that a murderer was present at the time of the death. One very popular method is for the murderer to be the first on the scene and remove critical evidence of the trap, e.g. to remove the shotgun and the string. This is very risky, though, since the police tend to take strong notice of the person who discovers the body, especially if he has any real connection to the victim.

This is a solvable problem, though. One approach to not having to be the first on the scene was done in the Sherlock Holmes story The Problem of Thor Bridge, where a simple machine hides the murder weapon. This approach has the downside of working best for disguising suicide, so it’s only available to a fairly small number of murderers.

Another solution to the problem of not having to be the first on the scene can be found in a Dr. Thorndyke story: the construction of a highly atypical weapon. In the story I’m thinking of, somebody fixed up a chassepot (a french rifle from the 1860s) to shoot a small dagger. The murderer then shot his victim from across the street. When the police looked for a man who entered the building to stab the victim—since knives or normally close-quarters weapons—various people in the building could swear that no one had entered the building since before the actual murderer was last seen in public, giving him a cast-iron alibi. This works, though its solution could easily be too technical to be widely enjoyed. The other problem with this kind of solution is that the murderer must either be very lucky and trust to his extreme luck, or else he’ll have to spend a lot of time, in private, perfecting his weapon for it to be reliable enough to be accurate at twenty or thirty yards. Accurately launching projectiles is simply not easy. If the first approach is taken, the story will lack plausibility. If the second is taken, the murderer will need access to a lot of private space for a decent amount of time, meaning he must have a fair amount of resources at his disposal. This reduces his possible motives for murder, since it can’t simply be money (it could still be money in a complex way) and whatever the motive, it must be a very long-lived one for him, not only to go to so much trouble, but to consider murder a viable solution to his problems for so long a period of time.

Of course, if all this seems too complicated to the murderer, a trap which is undisguised can be paired with framing someone else for setting the trap.

I suppose I should mention the other possibility, which is to attempt to hide the trap. This is viable so long as the trap causes death in a way that can look like something else. An example of this would be a trap that hits someone on the head at the top of the stairs, causing him to fall down the stairs. The blow to the head could easily look, post-mortem, like an injury sustained during the fall. The murderer will need to construct the trap very carefully to not be obvious, at least for a time. It’s a great risk to permanently leave the trap in place, but if it can pass without notice for a few days, that would give the murderer an opportunity to retrieve the incriminating bits later, after attention has faded from the murder scene. (Alternatively, the trap can be made with biodegradable pieces and put someplace that water or wind will eliminate the evidence.) This last part can be fun because the bits that don’t quickly pass away can catch the eye of the detective while looking like not much of anything to people with less imagination.

Considering it all, I think that, for all their difficulties, traps are still workable in a modern mystery. A fair amount of care will need to go into the construction of the murderer who employs a trap. It can easily seem unjustified. This is, to some degree, a result of murder mysteries being primarily novels rather than short stories; in short stories you can leave enough of the character up to the imagination of the reader that he can simply trust that the character’s backstory makes sense for doing murder with great self-control and resourcefulness. (This last part can be ameliorated somewhat by having the murderer copying something he read about rather than coming up with the idea himself.) Novels require greater consistency in their characters since there is more of the character in a novel than in a short story. Still, I think it can be done.