The Midnight Practical

The morning of the final anatomy exam, the university lab became a crime scene. Adrian, the class valedictorian, was found dead on the floor, his throat slit by his own hand. On the steel table above him lay his roommate Billy—surgically disassembled with such terrifying precision that the police initially thought it was a cadaver, until they identified the face. The third roommate, who found them, hasn't spoken a coherent word since. Who took the test?