In my on-going study to create more believable antagonists, I’m studying the book The Anatomy of Motive by John Douglas and Mark Olshaker. The chapter I’m in now deals with people in the workplace who, for no apparent reason, snap and kill their co-workers, bosses, even themselves. It also applies to students who enter their school campus and go on killing rampages. A large portion of this chapter is case studies, but I found a section that’s useful for writing purposes.
Douglas says that most people don’t snap. It’s not a common occurrence. So when it does happen in your novel, it needs to be as realistic as possible. To figure out if the antagonist is going to snap, you can’t have your protagonist sit down and interview him. Most people won’t open up about personal problems to anyone, not even close friends, so it won’t be realistic. Instead, have your protagonist analyze the antagonist’s behavior.
“What is this person’s normal behavior? Is that what we’re seeing? Have there been changes? Is he suddenly becoming obsessively religious after having been unobservant in the past? Was he a social drinker who is now either displaying signs of inebriation or, alternately, criticizing others who are droning and not going to church? Is he complaining about others in a way he never did before? Is he obviously eating more or eating less? Is there a change of pattern?”
You’re looking for someone who’s life is no longer in balance. If you’re creating this character, you’ll need to be subtle enough that tons of people don’t notice and get scared, but not so subtle that no one notices. Most of the time, motive in these cases is anger and revenge. They are always quick to blame someone else for the tragedy, and are usually organized. They plan their killing sprees, as opposed to one day rising from their chair and grabbing a weapon of opportunity.
This chapter didn’t help me much in my writing, as I’m not planning to have a character snap in any of my books. But some of the information can easily be applied. Behavior watching nets a ton of useful information about a person. I image the normal everyday behavior of a serial killer is vastly different from a soccer-mom housewife. Or maybe it isn’t. That’s the scary part.