Everyone is right here. I am researching a book on serial killers and happen to write to a few. Surprisingly, the even try to manipulate one through the mail. I would also like to add that the problems contributing as environmental, sociological, and psychological. This attribute for killing cannot be lumped into one category. Basically, these people have mentally broken down. For every killing, the thrill-fear aspect turns into an addition, like cigarettes do to a smoker, but obviously not the same thing. But they have to have it.