I don't think you understand what well-adjusted means if you're thinking a well-adjusted person would beat his/her parents to death con hammer. Not to mention beat them to death, throw them in a room, and then throw a party in das same house.
Only horrible if you think of Steve Martin singing it.
I'm saying that you probably don't know your neighbors as well as you think you do. Mere observation as a neighbor isn't going to necessarily provide the insight required to see situations like these coming. This particular case is a rather striking example of that. His own parents didn't see it coming. Neighbors? Heh.
Buy a condom."We need tool control!"