Another angle would be to have some sort of generator situation, where he figures out that if he kills a particular Demon or destroys a machine or something big like that, he stops the entire outbreak. That scenario would give him the satisfaction of getting the best scenario win out of this (especially if the zombie return to normal people when the source is destroyed). I ran a game like this once, and it was disturbing for the players becasue between all the moans the zombie would manage to wheeze out a "heeeeelp meeeeeeeee" to the players at times. They didn't wanna shoot or kill the zombies and had to play a game of outrunning and out manuvering them until they found the source.
