Not that I'm justifying what he did at all, obviously, but I'm pretty sure it was actually WoW, and he said himself that it had no influence on what he did.
His motivation was predominantly political, and also psychological. Some people genuinely believe that what they're doing is for the good of mankind, or that they are prophets chosen to spread the "good word". There was a crazy homeless guy in Hastings last week who thought he was the next Jesus, and was going around shouting "YOU WILL NOT BE SAVED" and "DEATH" at random people (including my Catholic mother), insisting that God had told him so.