It took you a waste of your power to figure this out? The fact that he found the serial killer didn't tip you off? What other possible role could he be? The only thing I could think of is Mafia Cop, and your test wouldn't have proven it either, since it would have blocked the mafia kill as well. Now, I don't think he is a mafia cop, but I never did, and I just don't know why you still suspected him after he stuck his neck out to get the SK yesterday.