My conclusion was that he is an alien, the tests they did on his eyes re being able to see UV was never explained or his incredible knowledge re the planets etc. I think the regression was a red herring in a way as up until that point i firmly believed he was an alien but then the regression puts a spanner in the works, but i think they are saying that infact he used the other guys body / was linked to him in some way..? clever film great acting..