I think events like shootings and robberies by unusual suspects, like elderly women, occur due to something called “permission giving.” A kid shoots up a school. Two things occur in the mind of other kids. One is how famous the shooter is and the second is, if he can do it, I can do it too. As to why, I’d suspect that most if not all the shooters are sociopaths. They have no sense of how other people feel. Not all sociopaths are evil. I read about a clinical psychologist who was examining brain scans in a study of sociopaths. Unknown to him his associates had slipped in his own scan, and he diagnosed himself as a sociopath. (As I recall a sociopath has a distinct lack of activity in a particular area of the brain.) When this became known and he was interviewed he said something like, yes, I knew I had no connections with other people. When Aunt Tilly died, I decided I’d rather play golf than go to the funeral. I knew it was “wrong” I just didn’t care. He was a successful doctor and father.
Socio and psychopaths tend to make the most ruthless and sucessful CEOs.