The ending feels tacked-on. (Spoilers I guess)

I always got the feeling that the whole possession thing was an after thought and that the orginally there was a actual human killer. Lets face it, why would someone possessed by a spirit walk around in a dive suit killing people unless they didnt want their identity known? Plus, when the house mother gets it on the staircase, the killer is seen wearing heavy boots. That doesnt make sense. There are other things bothering me as well about the ending. As much as I love slashers, this one has me on the fence.

So if the killer was originally going to be human, who would the killer be?

I like guns, slasher movies, and more guns.