Why mommy, why??

How do you explain to your 4.5 year old why attrocities such as today happen? I must confess that I was at a loss. I stumbled along talking how we all have different views and beliefs and are entitled to them but that sadly some people feel that the only way to make their views known is to create chaos. He seemed satisfied with this and didn't question any more and didn't ask any more specific questions. My heart goes out to everyone affected by today's events. I hope they catch whomever is responsible for the bombings, though realistically they probably never will.