There’s a mix of nature and nurture in determining the behaviors of anyone.
For much of this century, psychiatry and psychology overwhelmingly focused on nurture. Parents were blamed for schizophrenic children.
It’s become abundantly clear in the last couple of decades that severe mental disorders like schizophrenia and autism are almost entirely nature and have NOTHING to do with how a parent raised a child (schizophrenia is genetic, and also possibly related to odd things like a disease acquired from cats. etc.)
That said, in terms of serial killers (remember to differentiate from mass killers), ALMOST all of them underwent severe abuse by a parent in childhood (the striking exception is Dahmer where no evidence has ever been uncovered of abuse, and Dahmer was torturing and killing animals at a very young age.)
A lot of people are very emotionally (or religiously) resistant to the idea that something like genes or a medical condition can determine your behavior. There are a shocking amount of people on FR who seem to literally not believe mental illness exists as a medical disease (but yet believe in things like demonic possession, despite this being the year 2012, not 1402, last time I checked.)
“A lot of people are very emotionally (or religiously) resistant to the idea that something like genes or a medical condition can determine your behavior.”
I read today (NY Post article, I believe) where, in addition to the autism/Asperger’s problem, Adam Lanza had some kind of physical condition which prevented him from feeling pain (at least some types of pain).
I also recall that in high school, they kept an eye on him in the tech club because they were afraid he might burn himself with a soldering iron (and not be able to feel it). I also recall reading where his mother had problems with his trying to burn himself with a cigarette lighter (perhaps in a quest to find out “what a burn felt like”?).
It’s almost as if his nervous system wasn’t “internally wired” properly to the brain...