There is laveyan satanism, read about it. Satanism in its theistic form is pure bullshit, for obvious reasons. Believing in any form of diety to the point that you want to hurt others in the name of it is insanity, regardless of what that diety would be - allah, god, satan, same old bullshit.
It's irrelevant, bottom line is he did what he did because he was a crazy ass modafaka. If you hurt others it has nothing to do with what you believe in, it's either your natural instinct or it's not. I would never hurt anybody, even though I sometimes imagine doing it not because it's against my moral code - I have no moral code, it's just not in my nature. I run from fight, I don't hurt anyone even when I can and want to. When I hurt someone emotionally I feel terrible about it. Again - not because there is something I believe in, some sort of conscious morality I follow, it hurts me like it would hurt me if I got bitten by a dog.