The killer is Alex the younger brother of Robin the girl that fell from the window years earlier when her classmates' practical joke got her killed. Alex secretly followed his sister and saw her demise and her so called friends cover it up. The last on his "death list" to be "punnished" is Nick...his surviving sister's longtime boyfriend (all the others and their loved ones are slain). During the crowning ceremony Lou...Kim (Alex's sis)'s bitter ex who got suspended thanks to Alex...stuns Nick and takes his place. By doing this Alex not fully aware it's not really Nick ends up decapitating him sending his severed head rolling out onto the walkway causing a panicked stampede. Kim finds Nick and tries to help him to safety, but is confronted by Alex. He attacks Nick and they struggle on the ground, Kim grabs the axe and when she's sure her boyfriend is out of the way, she strikes Alex in the head. Alex still masked turns around, Kim is able to get a good look at his eyes seeing how familiar they are to her, she suddenly realises in horror that she has just struck her own brother. Alex stumbles outside of the school and Lt. McBride points a gun at him. Kim runs out and tells the officer not to shoot. She bends down, takes the mask off her brother and cradles his head in her arms. He's wearing smeared lipstick on his face. Before he dies, Alex cries out that he saw what happened six years ago. "They did it," he says.
Revealing mistake: During the scene in which Lou forces himself on Kim in the lunchroom, donning a black ski mask, Kim's brother Alex jumps up to his sister's defense. Just before Alex throws his first punch, Kim screams "Michael," referring to the actor's real name Michael Tough. Kim then correctly screams "Alex," the name of the character he was playing in the film.