they were born into dire poverty, have nothing going for them, and really don't have a purpose in life. The costs of doing something horrific is relatively small.

It's always surprising when someone who has it all going for him does something horrific. Being affluent, having a great job, great relationships, kids, etc should stop a person from doing something that would wreak havoc on everything they've built. Nonetheless, sometimes people can't help themselves and will go to any measure to cover up what they've done.