***spoilers***Who killed who?
Steve: Stu
Casey: Stu
Sidney attack at her house: Stu
Bathroom attack: prankster
Mr. Himbry: I'm inclined to say it was more a thing for Stu to do. But I'm just going with Billy, because otherwise he doesn't have many killings on his list and Stu was busy preparing his party.
Tatum: Billy
Kenny: Stu
Dewey attack: Billy