What makes a person go "boom"?

Recently, I was watching ID (Investigation Discovery) Channel while I was putting my clothes away and doing some other mundane chores. Over the course of several hours, they had some different shows on there about tradgedies that have happened in our country, such as the Waco texas incident, the fiasco with Lisa Nowack the diaper wearing astronaut, and the shooting at the amish school house. It struck me that people are volatile. I mean how can you really know someone and trust them? Lisa Nowack had it all. She had young children, she was an astronaut which was something she had wanted to do since she was a child. Jealousy would be her downfall. She lost it all over a momentary lapse of judgement and common sense. Charles Roberts, the gunman that took the lives of five little girls as well as his own, was a normal man who had small children of his own. He had lost his first child, and was very bitter against God, and so his outburst was caused by his deeprooted rage. As far as David Koresh...well I just think he had issues from the get-go. But I really am beginning to put some serious thought into the idea that we are all sinful people, and that deep down we are all capable of things that would shock the world. I was raised a christian, and so I believe that we all need the gift of Salvation, but I think that the world continues to be shocked by the things that people do and it seems that people want to believe that deep down we are all good people. I agree that some people seem to have no conscience, but then what about people who seem to just suddenly snap, and do things totally out of their character? Is it because their brain is "broken" suddenly, or because we all have a sin nature and are just as capable as the next person of doing bad things? Something to think about.....