Stu Was The Sole Killer?!
What do you think of the theory that while Billy killed Maureen (as Stu watched), it was Stu that actually committed all of the murders as Ghostface? Like, imagine Billy's role was akin to Manson's involvement in the Tate-LaBianca murders, where he masterminded everything, chose the victims and arranged how everything would go, but left the dirty work itself to his patsies (in this case, Stu.)
Just go back and re-watch: Stu has the motive to kill Casey and Steve. He runs right back to the school right before Himbry is murdered. Ghostface goes inside the house after Tatum is murdered (makes no sense for Billy to do that.) Kenny is obviously murdered by Stu, since Billy faked his death just minutes prior.
What do you think?