Marli Renfro wasn't famous, but she played a part in one of the most iconic scenes in American film - as Janet Leigh's nude body double in Alfred Hitchcock's Psycho. Only hours after seeing the film, a young man dubbed the "Psycho Killer" took the life of his first victim. Then Marli inexplicably vanished, leading to reports that she'd been murdered. For Robert Graysmith, Marli's fate became an obsession - a personal love note to a beautiful dead girl.