What do you find more interesting, trying to figure out who done it or why they did it? As far as police techniques, it seems that that wouldn't vary too much from story to story. But wouldn't it be more interesting to delve into the mind of a serial killer?
Serial killers and their minds are old hat. I don't see any hope of new plots there. As for mysteries: I always want both.
I do have a new take on serial killers, but that's down the road.
I've thought about this question a lot, which is one reason I made my protagonist a bounty hunter. Grace deHaviland always knows who she's chasing. The question typically is why did they jump bail? Also, why did they commit whatever crime they committed (or are accused of committing) in the first place? I think the answer to that can lead to nearly unlimited reasons, and thus limitless story possibilities.
Yes I think the why is very important. Also the conscience. Psychological suspense is enhanced when the detective plays a cat and mouse game with the suspect.
Both who and why, but especially with old and unsolved cases. It's the challenge of the most difficult cases that intrigues me most. The pressure of time constraints, schedules, etc., are not there, usually, so it's more conducive to an independent, maybe unconventional, approach, along with the standard practices.
The why is always more interesting than the who. What I have trouble with is the ease with which too many murderers can bluff their way around the initial investigation. It seems to me that murder ought to be a monstrous act which should cause great anxiety, shame, guilt and fear. There can't be as many sociopaths out there as we find in fiction. I hope.
There certainly aren't as many brilliant criminals. That's an invention of mystery writers who want to give their protagonist a really challenging case.
For this reason, I generally prefer police procedurals to amateur detective novels. In a police procedural, you get a variety of cases and many are closeer to the real world.
I'm trying to strike a balance. In my contemporary stories, the protagonist is a crime reporter. As I have been one for 20 years, I know a little bit about it, and have even aided law enforcement on rare occasions.
The problem with real criminals is that most of them are flaming stupid. You have to come up with smarter ones just to have a story.
But even if a serial killer is a lowlife and uneducated, there must be something interesting to say about him. I'd like to probe deep into a deranged mind.
There might be, but there might not be. Maybe Hannah Arendt was right about the "banality of evil." There's certainly a lot of books about serial killers, there's a new one just out about Charles Manson, but it is possible that most of these guys aren't very deep or very interesting.
Of course, you could still write a good book on the subject. Although I have to admit, I find the interest in serial killers more interesting than the killers themselves.
Well, surely it's the money. Right? People like to read horror, serial killings are horror, and that sells a lot of books (and films). Not all that interesting, unless you are thinking of the dark underbelly of the average reader's psyche. But we've always known that people love to see blood and torment. I.e. the Romans! And human sacrifices in ancient times. It's all very uncivilized. Maybe we're returning to some bestial state.