You know that dramatic reveal at the end of a good mystery where the sleuth explains who committed the murder and why? **SHOCKER!** The author had all those details worked out well before the first page. A good mystery writer begins the book knowing the murderer’s method, motive and opportunity. And all those elements must logically add up, else readers will be very unforgiving – and very vocal — in reviews.
So when I’m considering a character to commit murder, these are my considerations:
Is this character obvious – or will the identity be too easy for readers to deduce? If so, I know I’m going to have a lot of work to do. The husband, for example, is naturally Suspect #1 in his wife’s murder – and it’s okay if he turns out to be the one who did it – but there better be a lot of doubt in the reader’s mind.
Is the character physically capable of committing the murder? That doesn’t just mean physically – which he or she must be – but also emotionally. The murder must fit the murderer.
Does the motive make sense and is it believable? Granted, there is a certain allowance for suspension of disbelief in all murder mysteries, but the motive must still carry some weight. A good mystery is telling two stories: the one on the surface – which your sleuth is engaged in solving – and a darker, hidden story buried between the lines. That story must be equally engaging.
Does this character impact the story (besides being the catalyst) and leave an impression on the reader? The murderer doesn’t have to be a main character, but should at least be a supporting role throughout the book. There’s two things you can’t do – introduce the murderer at the beginning of the book to never be mentioned again or introduce the murderer in the last quarter of the book. Both of those strategies are cheating. The murderer must be visible, interacting with the main characters of the book and known by the reader fairly early in the story.
Even if the answers to a couple of these questions are no, I may move ahead with my plot—but I know that I still have a lot of work to do. Still, if the character just doesn’t feel right, I might explore motives for the other character. In Prey of Desire, the identity of the original murderer changed for the better. Both characters were still in the book, but only one character brought all the elements together for a good murder mystery.