Well, I've come across articles saying some mentally disturbed people commit such activities cuz it gives them the perverse satisfaction that they actually have the power to take lives. Having the power over one's life. It makes them feel like God or something. It's like, punching walls, doesn't make them feel better cuz a wall makes no sound, have no expression, won't feel pain, is basically not alive.
Anyway, I don't ever wanna get into their minds to find out what those guys are really thinking. I just wish they'll meet their maker in the worse ever way possible. Heh.