Haniglos Lanu Ulivaneinu. I’m glad it’s not my job. Elokim Yir’e Laleivav.
I don’t understand the mind of a murderer (luckily), and I don’t really want to. Forensic psychology sounds like fun but who would want a glimpse into the worst trains of thought? Hashem measures everything. Even the child killer had weirdness that’ll be put on the scale.
As for us, a Rasha is a Rasha, unless he qualifies as a Shotte. Perhaps he had a hard upbringing, perhaps he got himself all worked up into a mad frenzy, perhaps he read some strange philosophy book that justified murder, or he heard a speach from his leader calling for it. So what. Kill him — or whatever the current, local, law is.