The evil Carol Arlington
Carol Arlington (Amanda Blake; 1929-1989) is the villainess from "Whodunit," episode 1.26 of Alfred Hitchcock Presents (airdate March 25, 1956). She is the wife of murdered author Arthur Arlington, who was sent back to Earth by an angel to solve his own murder. Carol was revealed to be having an affair with her lover, Wally Benson, mainly due to feeling neglected by Arthur.
Carol was revealed as the killer as she was being questioned by Arthur, as were Benson, Talbot (Arthur's secretary) and Vincent (Arthurs nephew). During the questioning, Benson shut off the lights, allowing the evil Carol to stab Arthur to death. Back in Heaven, Arthur figured out that Carol killed him due to the fact that the murder had to have been committed by someone Benson trusted. As revealed by Hitchcock, both Carol and Benson were arrested for Arthur's murder.