Hmm.  I'm not certain your reading this correctly.  If he was a possessing spirit, what prevented him from possesing one of us?  I think it certainly was supernatural, but more in an Obi-wan/Sauron kind of way... becoming an astral being or something like that.  Perhaps it was a last effort of will, perhaps we've just created our first reoccuring villian.  I'll do a knowlege Psychic check in thread.