It’s called evil. Theodore Dalrymple is right in the piece excerpted below about science having no explanation. You can read about evil and learn everything you need to know by reading the Old and New Testaments of the Bible. From City Journal:
By a strange irony, alleged Aurora mass murderer James Holmes was a doctoral student of neuroscience—the discipline that will, according to its most ardent and enthusiastic advocates, finally explain Man to himself after millennia of mystery and self-questioning.But what could count as an explanation of what James Holmes did? At what point would we be able to say, “Aha, now I understand why he dyed his hair like the Joker and went down to the local cinema and shot all those people?” When we have sifted through his biography, examined his relationships, listened to what he has to say, and put him through all the neuropsychological and neurological tests, will we really be much wiser?