Two things I want to point out in this discussion:
1. You can't necessarily understand how he thinks without knowing if he has a personality disorder. Same with school shooters. Same with mass shooters and spree killers. A personality disorder changes everything.
Additionally, you need to take psychopathy into account. Most, if not all, SKs would be considered psychopaths. And psychopaths, often having one or more of the 10 personality disorders, simply don't think like everyone else.
So yes, we need to try to understand their way of thinking. But that is very complicated, because they don't exist on the same plane that most people do. That's why you'll often hear psychologists describe specific serial killers as "inhuman" or "devoid of personality."
2. He is not necessarily raping them, or even having sex with them!! Sexual killers don't usually have sex the way the rest of us do. It is not at all uncommon for them to get their rocks off on the act of killing itself, or some other thing they do to the victims that has a sexual charge for them, even though it seems nonsexual to us.
Consider all this IMO, even though I can site everything I said if I really had to. ;-)
ETA: I wrote this post before while I was sitting in a waiting room, and I'm afraid it's a little sloppy! Two clarifications:
1. When I say that sexual SKs don't usually have sex the way we do, I mean
with their victims. Of course they can have "normal" sex, as well.
2. Sorry if I sound a bit rigid in my thinking. I have outside expertise on mental and brain health, and that is what I'm drawing from here.
