Shot at Virginia Tech

Already you know, a man killed 33 students of Virginia Tech including himself April 16th. I watched this news on TV in Japan, and it was a terrible shock to me. Why must he kill another students? What makes him be murderer? Didn't he have another way sure? I haven't been able to understand him and I haven't believed this incident yet .But the same time, I have know that this is the unmistakable FACT. Although everyone know (I think) that killing someone is bat thing absolutely, murder cases cannot vanish but be increasing. How to creat peaceful world? How to make peaple become happy? What should I do and What can I do for these dreams? Now, If you were asked that the reasons why we mustn't kill someone, how do you answer it? Can you answer this question? Please gime me your reply. I pay victims' last respects.