The Coincidental Killer

I’ve been researching  serial killers this week. It’s not one of my favorite things.
 
Not that I don’t enjoy the chilly creepy pleasure of the occasional serial killer thriller, but too often serial killers are used as a means of having to avoid writing a real mystery. These fictional serial killers always make it easy for the detectives by contacting them first because they’ve inevitably formed a weirdo attachment and they’re planning the de rigueur cat and mouse game in which the serial killer does all the real work.
 
I’m not saying that can’t be entertaining. Sometimes it’s very entertaining. There’s a reason serial killer stories continue to sell well.
 
Part of the horror of real life serial killers is that -- like other forces of nature -- there’s no real way to guard against being randomly targeted by a lunatic. That’s also part of the fascination. It’s like spontaneous combustion. The chances of it happening are phenomenally slight, but at the same time there aren’t any real preventative measures you can take. Don’t eat too many jalapeño peppers?
 
Well, let me qualify, there aren’t any real preventative measures beyond the preventative measures we all hopefully take on a regular basis. Lock your doors, don’t walk alone at night down a dark alley, etc.
 
What is more preventable are the crimes that occur simply out of bad luck and the opportunity for evil. The night you have a fight with your boyfriend and go to a bar...and end up giving a stranger a ride home...that's arguably preventable. But someone’s car breaking down on a lonely stretch of highway -- nine times out of ten this results in nothing more than a long walk and a lousy night. But every so often, bad luck and evil collide.
 
Black coincidence. A different day, a different hour, sometimes a matter of minutes can make the difference between life and death.
 
Of course fiction is not real life and the number of coincidences a reader can swallow are fewer than might occur in real life.
 
Also, although smart people do dumb things, in fiction the dumb things have to be believably dumb. Also limited in scope and few in number.

 
Anyway, I’m not sure what my point was. The fact that humans are capable of vile and depraved action is not news. Humans are also capable of heroism and self-sacrifice. Evil and insanity are over-represented in fiction. From a reading standpoint, I prefer small, intimate stories over grand scale slaughter. Motive is the single most interesting element to me in any crime story. Crazy is not a motive. But when you write, you have to mix it up.
What do you love in mystery stories? What makes your scalp tingle and your pulse thump?  Do you intricate puzzles or romantic cozies or bloody thrillers?