One of the first things people say after a horrific crime is committed is: why? Investigators are trying to find a motive for the young man who killed little schoolchildren. Finding a reason for a behaviour does not mean you excuse it. You find a reason for why it happened because it might provide insight into how to prevent it from happening again. In some cases understanding a behaviour allows people to achieve forgiveness, which can be important towards healing.
Fulltime student posted an article by a respectable paper which tries to do exactly that - provide information that could give some insight into why this person did what he did. The OP is not condoning the action in any way by trying to find an explanation.
There is never any excuse for rape, brutality against women, murder. Understanding why it happens is important.