ATPG scanned as a bodyguard.

I agree that one of the doctors is likely to be the killer. I've got a whole lot of hypothetical's - 'if Player A is scum, then Player B should be cleared,' sort of things - running through my head, but frankly none of them seem to be yielding anything with the information that is currently known. Thus I'll go with the doctor who has exhibited the most unusual behaviour:

vote: Chaotix

Extremely reluctant to go along with the mass-reveal earlier, scanned as a bodyguard but claims a pure doctor role, and supposedly blocked twice in a row. It just doesn't seem to add up.