I commend you for your well-written post. You demonstrate clearly and eloquently how many people have a skewed perspective when it comes to dealing with such a difficult and delicate issue.
Surely you are right that some people feel the need for justifying the crime. But another thing people need, and maybe this comes from that same place deep inside; someone to blame. How difficult is it to face a horrific tragedy when there is no one to blame? Having no one to blame can make life feel so meaningless and arbitrary, it can penetrate the deepest essence of a person.