This is a sad reminder of just how powerful and dangerous misogyny and sexism still is in today's world.
This man was a product of a society that promotes the belief that a man is entitled to sex and attention from women; a society that says that a man's worth is determined by sexual conquests and violence/domination. Since he couldn't achieve the former, he resorted to the latter.
An excerpt from his manifesto, which you can read here: http://www.scribd.com/doc/225936731/Untitled