They marched into battle so loaded with fear and mysticism that insanity was the only way out. Utter disregard for life. The same with Hitler, or Stalin, or Yassar Arafat. If one is living in constant fear of death, it seeks you. And in the meantime, you take pleasure in killing others.
Killers have reasons, pain, goals, genius and rights.
They come from every walk of life and most of them enjoy dogs, children and religious ceremonies - unless the children are too inquisitive or the ceremonies too frightening. They feel comfortable with everything that is familiar, terrified by themselves, and desperate to demonstrate their courage. I have been all this. It nearly killed me. And so, death is not just something that falls on you because you weren't paying attention, or because you drove in a reckless fashion.