Are you aware that the human brain doesn't stop growing until the age of 25, and that the last part of the brain to develop is the part that gives a human being a sense of empathy? Perhaps he has no empathy right now, but will develop it later, and realize the awful thing he did.

Also, I stated that there is no justification for what he did. But there are factors and reasons for EVERYTHING that EVERYBODY does, and to say that you don't care why people do the things they do shows a level of ignorance that unfortunately is very pervasive is today's society. People are afraid to know why bad things happen. They just want to believe that evil exists, and that it should be squashed by any means necessary, no questions asked. It is a very archaic way of thinking.