I know the person who try to kill (killed several times :P) Tree is Lori Spengler in the film. We find it out at the end of the movie.
At the first time when the killer shown and killed Tree he looked like a man, may be the movie makers want to confuse us.
And Lori is a slim girl. So I was wondering, is Ruby Modine aka Lori really acted as killer in all scenes? ( we see she removing the mask, when Tree tells she was the killer) or was it some other person?