Suspense/Thrillers vs. Whodunits

As I was watching last week’s DVRed episode of Castle, I got to thinking about how one of the primary differences between suspense/thriller type mysteries and more classic whodunits is the type of antagonist.  Suspense/thrillers seem to so often have serial killers or serial offenders of some type at their core.  I won’t risk saying they all do, though most I’ve read in recent years have fit that mold (I love that kind of story, so it’s entirely possible that I gravitate toward them).  Your more classic whodunit, whether a noir or a cozy seems to focus on the less…I was going to say complicated, but that’s not the right term.  But whodunits seem to fall more into the realm of a single or handful of killings that are for a purpose, to cover something up rather than as an escalation of some sick man (or woman)’s fantasies.  Now regardless of type of bad guy, motive can be all over the board, though the classics are the usual sex, money, jealousy, power.  But with the non-suspense/thriller type of mystery, the motives seem often less psychologically complex.  That doesn’t mean a less complicated plot or a less interesting one, just not the same kind of experience as spending lots of pages crawling around in the mind of a serial killer.  I probably don’t want to analyze why I tend to read the latter kind of book…

While I have read a lot of mysteries (my love of reading was whetted on Nancy Drew and Hardy Boys), cozies in particular, I’ve never written one.  I’m not sure I’d know where to begin.  Knowing me, I guarantee I would complicate the heck out of it.  The complex forensic psych profiles I tend to write up for my killers would not quite be the order of the day for a cozy villain.  I mean, obviously, I’d need to know his/her goal, motivation, and conflict, but as to deep personal analysis–I’m not sure if it’s necessary.  So often you don’t actually see the villain in that kind of mystery.  It’s more that somebody’s dead (or something else happened) and now the hero/ine is playing Sherlock Holmes to find out who did it.  The face isn’t revealed until the end.  And so often, the perpetrator ends up being some normal person under extraordinary circumstances.  Not someone with a sick or twisted mind.  Maybe in some ways those are the scariest sorts of mysteries.  The ones where we can really identify with the killer because his wife cheated on him or she’s losing her business or whatever.

Anyway, what’s your thought on this, reader?  Do the killers for classic whodunits have to be as psychologically complex as a suspense/thriller?