Raising Cain (1992)

Dr. Carter Nix is a respected child psychologist. His wife, Jenny, becomes concerned that Carter is obsessively studying their daughter, Amy; he regards her like a scientist tracking the development of his creation. But Carter himself suffers from multiple personality disorder; his alternate personalities include Cain, a violent petty criminal, Josh, a shy 7-year-old boy, and Margo, a middle-aged nanny who protects the others at all costs. Carter and Cain are killing young mothers to procure their children, apparently for experiments performed by Carter’s father, a child psychologist who lost his license years earlier after performing unethical experiments on children.

Jenny is having an affair with her ex-boyfriend Jack Dante, the widower of a former patient, and she plans to leave Carter for him. When Carter discovers their tryst, Cain takes over and begins leaving subtle clues for the police implicating Jack in the murders. Next, he attempts to kill Jenny by suffocating her and submerging her car in a lake. She escapes, however, and confronts Carter at home. Unable to find Amy, Jenny demands Carter tell her where she is. Carter replies that she is with his father – only for an incredulous Jenny to reply that his father has been dead for years.