Re-Animator

At a medical school in Zurich, Switzerland, a dean is called in to investigate a disturbance in one of the labs. When he enters with a policeman and nurse they find one of the school's professors, Gruber, screaming in agony and a med student, Herbert West, with him. Gruber's skin has turned purple and his eyes bulge until they explode, spewing blood. The stricken man falls dead and the dean asks if West had killed the doctor to which West replies "No, I gave him life!"West arrives at Miskatonic University in New England in order to further his studies. He rents a room from medical student Dan Cain (Bruce Abbott) and converts the house's basement into his own personal laboratory. There is an instant animosity between West and faculty member Dr. Carl Hill (David Gale). West declares that Hill stole the theory of brain death from West's late mentor, Dr. Gruber. Hill vows that West will never get a passing grade in his class.Dan has been carrying on a clandestine love affair with Barbara, daughter of Miskatonic's medical school's dean, Dr Halsey. Barbara and Dan know that if her father finds out about their relationship, Dan could be expelled.Dan discovers that West has re-animated his dead cat, Rufus, with a glowing "reagent." West recruits Dan as his partner in research to defeat death. Dan's fiancee Megan dislikes West, especially after discovering Rufus re-animated in a state of dismemberment.Hill manages to turn Dr. Halsey against both West and Dan. Barred from the school, West and Dan sneak into the morgue to test the reagent on a human subject in an attempt to salvage their medical careers. The corpse revives and goes on a rampage, attacking the duo. Halsey stumbles upon the scene originally to force them out of the morgue for trespassing and, despite attempts by both West and Dan to save him, is killed by the re-animated corpse. Armed with a bone saw, West dispatches the reanimated cadaver. Unfazed by the violence and excited at the prospect of working with a freshly dead specimen, West injects Halsey with the reagent. Halsey returns to life, but in a zombie-like state.Hill discovers West's work and gains guardianship over Halsey, whom he puts in a padded cell adjacent to his office. Dan and Megan break into Hill's office where they find evidence that Hill is obsessed with Megan and has lobotomized her father. Hill has gone to confront West in his basement lab and threatens to blackmail him to continue his research so that Hill can take credit for West's reagent. While Hill is distracted, West hits then decapitates Hill with a shovel. Overcome with curiosity, West re-animates both Hill's head and body. While West is questioning Hill's head and taking notes, Hill's body knocks him unconscious. The body carries the head and steals West's reagent, returning to Hill's office. Exercising mind control over Halsey, Hill sends him out to kidnap Megan from Dan.West and Dan track Halsey to the morgue, where they find Hill's body holding his head in a compromising position over a restrained Megan. West distracts Hill while Dan frees Megan. Hill reveals that he has re-animated and lobotomized several corpses from the morgue to do his bidding. However, Megan manages to get through to her father, who fights off the other corpses long enough for Dan and Megan to escape. In the ensuing chaos, Halsey is torn to pieces by the corpses after he destroys Hill's head and West injects Hill's body with what he believes is a lethal overdose of the reagent which began to destroy Hill's body. Hill's body mutates horribly and attacks West, who screams out to Dan to save his work as he continues fighting. He is dragged toward the monstrosity, his fate unrevealed.Dan retrieves the satchel containing West's reagent. As Dan and Megan run from the morgue, one of the re-animated corpses attacks and kills Megan. Dan takes her to the hospital emergency room and tries in vain to revive her. In despair, he injects her with reagent. Just after the scene fades to black, Megan screams, implying that her re-animation has backfired.

Question: Who did the corpses tear to pieces ?
Answer: Halsey