The Woman Is a Stranger (1968)

Jay Delanay, the son of a wealthy American film producer showing a film at the Cannes Film Festival, suffers from psychotic disturbances. From his hotel room he spots through his binoculars a beautiful young starlet in a blue bikini. On the pretext of introducing her to his father, he lures her to his room and strangles her. When Sophie, his stepmother, discovers the crime, Jay forces her to keep mum. Other victims will follow...