Scream 2

While attending a preview of the film Stab, a film within a film based on the Woodsboro murders depicted in the first film, two Ohio Windsor College seniors, Maureen Evans and Phil Stevens are murdered by Ghostface. Phil is stabbed through the ear in a bathroom stall while trying to eavesdrop on strange whimpering noises. The killer, wearing a Ghostface costume, then returns to the screening and sits beside Maureen before mortally stabbing her. At first the audience believes she is part of the raucous acting out by audience members until she falls dead in front of the cinema screen.
The following day, the news media including local journalist Debbie Salt, descend on Windsor College where Sidney Prescott, a theatre major, now studies alongside her best friend Hallie and her new boyfriend Derek, fellow Woodsboro survivor Randy, and Derek's best friend Mickey. Sidney receives prank calls but is oblivious to the recent killings until someone instructs her to watch the news.
Two other Woodsboro survivors arrive at the campus: officer Dewey Riley to help Sidney, and reporter Gale Weathers to cover the case. Gale tries to stage a confrontation between Sidney and Cotton Weary, who is attempting to gain fame from his exoneration for the murder of Sidney's mother. After Gale forcibly brings Sidney to Cotton, Sidney angrily hits Gale.
Later that evening, Sidney goes to a party with Hallie. At a sorority house, Ghostface kills fellow student Cici. After all the partygoers leave, the killer then crashes the party and attempts to murder Sidney, though Derek intervenes. The killer injures Derek but Dewey and the police arrive, causing the killer to flee. The next morning, Gale discusses the case with the police. Upon realizing that Cici's real name is Casey, she concludes that the killer is a copycat who targets students who share the same names as the Woodsboro murder victims.
That afternoon, while Gale is talking to Dewey and Randy on the campus lawn, she receives a call from Ghostface hinting that he is watching them. They search for him, but Randy, who tries to keep the killer on the phone, is dragged into Gale's broadcast van and is stabbed to death by Ghostface. As night falls, Dewey and Gale review the tape of Ghostface killing Randy hoping to find some clues but the killer attacks them and seemingly kills Dewey. Gale hides and eventually escapes.
In the wake of the escalating murders, as two officers drive Sidney and Hallie to a local police station, the killer ambushes them and kills the two officers. In the ensuing struggle, Ghostface is knocked unconscious. After they climb out of the car, Sidney insists on unmasking him, while Hallie insists they escape. When Sidney walks back to the car, she sees that Ghostface has escaped. Sidney then witnesses Ghostface stab Hallie to death. Ghostface then attempts to attack Sidney, but she flees.
Sidney goes back to the campus and finds Derek in the auditorium tied to a crucifix and is confronted by Ghostface. The killer reveals himself as Mickey and kills Derek. Mickey details his plan to become famous in the ensuing trial and media spectacle. He then announces his accomplice, Debbie Salt, who arrives holding Gale at gunpoint. Sidney recognizes that Salt is actually Billy Loomis' mother, seeking revenge for her son's death. Mrs. Loomis betrays Mickey and shoots him, as she plans to pin the murders on Mickey. Before he collapses, Mickey accidentally shoots Gale, causing her to fall off the stage.
Sidney and Mrs. Loomis fight, until Cotton intervenes and eventually shoots Mrs. Loomis in the throat. When they see that Mrs. Loomis is still breathing, they find Gale still alive. Mickey suddenly jumps to his feet, but he is shot to death by Sidney and Gale. Sidney then turns and shoots Mrs. Loomis in the head and finally kills her. When the police arrive the next morning, Gale finds Dewey badly injured but alive and accompanies him to the hospital. Sidney instructs the press to direct questions to Cotton, rewarding him with the fame he has been chasing while removing the attention from herself as she leaves the university campus.

Question: Who stabs Hallie to death?
Answer: Ghostface.