For the mystery reader, discovering whydunit is often even more satisfying than whodunit.

When you pick up a mystery novel, you are making a decision about what sort of motive you prefer reading about, just based on the genre.

As with the type of sleuth and conventions surrounding the death itself, murder mystery does sort itself out by motive as well, surprisingly consistently along subgenre lines.

But before we get ahead of ourselves, we need to look at the primary question:

Why would someone bother to commit murder?

Murder is a tremendous hassle. Everyone in the world sees it as the #1 No-No, either because of ethics or due to the possibility of getting caught. It’s messy, upsetting, logistically challenging, and full of unpredictable elements that make it hard to plan.

Despite what films like Hitchcock’s Rope would lead us to believe, most people who puzzle in their heads about committing the perfect murder don’t go through the added work of actually killing someone to prove their theory.

So why do people do it?

As I see it, the reasons people murder boil down to these:

• Money: Someone kills to either gain money (stopping someone from changing a will for example) or to avoid losing money (perhaps someone getting rid of a business partner).

• Self-Preservation: This can be physical or more abstract, if someone knows too much and threatens to share what they’ve learned. An abused spouse might plot murder if they feel leaving the marriage isn’t possible, but so might a victim of blackmail, or someone who is aware of a witness to another crime they’ve committed. These murders have an “it was them or me” logic the killer clings to.

• Loss of Control: This is the “crime of passion” category, based on rage during an argument, a discovery of infidelity, and these are not premeditated. Emotion takes over and someone ends up dead.

These three usually operate between victims and killers known to each other. It’s difficult to claim “crime of passion” if you’ve never met the person before, so let’s consider two more, which are more likely between victims and killers who haven’t previously met.

• Obsession: In this case the target is often known by the killer, but not the other way around. Here we have serial killers pursuing a preferred type, people who harbour unrequited love for a celebrity and attack them, or other stalking cases. This can also serve as the premeditated version of Loss of Control- the jilted lover doesn’t blow up, but rather boils for months or years before killing.

• Ideology: People will kill if they have huge objections to someone’s political beliefs or actions, in the case of political figures. Religion can also be a motivation, as can the sense that killing this person will benefit humanity in some way.

Interestingly on this last point, I find it fascinating that “assassination” feels like a separate category. There is something more intimate about murder, and I can’t entirely place why. Do you consider assassination a type of murder? I’d love to hear thoughts in the comments.

How do these motives line up with subgenre?

I mentioned before my dramatic reaction to the first Scarpetta novel. A big issue here was the serial killer element. Part of what I find so disturbing about this type of murderer is the lack of personal connection in their motive. A victim may simply conform to a type they prefer, something the victim hasn’t chosen and can’t control. The murder itself is the sum total of the relationship between the serial killer and their victim, aside from a period of watching them and planning.

As I reader, I find this motive the most upsetting, and this appears to apply to the reading public as well. I have yet to discover a cozy mystery that included a cold-blooded serial killer.

Side note: Midsomer Murders also doesn’t count, because the killers are never profiling victims. In that show, even when we get over 10 bodies, there is nearly always a money or self-reservation motive that kicks off the spree, with nearly every additional victim a self-preservation cover-up.

On the cozy end of the spectrum, the whydunit is intimately connected to the relationship between murderer and victim. Rather funny that it’s less upsetting to think your family and friends might want to take you out instead of a stranger on the street, but the cozy reading public would be horrified to discover the killer was a random stranger passing through who simply had a taste for strangling blondes.

How this impacts the Iris Drake series.

Having studied psychology, the element of relationship and interpersonal dynamics is a big part of the appeal to me as a writer. I never intended to have a killer who didn’t know the victim, because the type of relationship that ends in murder was part of what fascinated me enough to write mystery.

That said, it doesn’t have to be a cozy simply because killer and victim knew each other. There are plenty of gritty crime dramas where the connection between the two is every bit as disturbing as the lack of connection a serial killer has.

Given my fear about serial killer psychology, I knew I didn’t want to write that sort of story, but I also didn’t want to make the story feel too much like a parlor-room melodrama. In addition, I do want to bring in elements of the thriller. Pages will hopefully turn quickly!

My most recent project has been creating a victim who’s made many poor choices in life, and surrounding him with a cast of people who all have solid motives to kill him. As I begin drafting the book, I have hunches about who might kill the main victim, but I also am open to the possibility that another killer may emerge instead.

Which of these motives fascinate you most? Do you notice that mysteries you read tend toward one or the other? I’d love to hear in the comments.