The other thing was about Mr Hengist. I never really thought about Scotty's body being used to kill the women, only that he was in close proximity and the killer more or less handed the corpse to him when done, there by leaving Scotty covered in evidence. If it feeds on fear, the fear Scotty had about being a serial killer could have been a between meal snack. Also, when the spirit left Mr. Hengist, Bones reports that he's dead, as if Mr Hengist was an animated corpse. So maybe that's why they didn't mind "killing" him.
I forgot about that: Hengist's body was dead when not inhabited by the demon. Good point.