Delirio caldo (1972)

Mr. Lyutak, a disturbed man with problems of sexual impotence, seduces a young woman in a seaside bar and kills her. Suspected of the murder, he is nailed by a series of damning pieces of evidence and arrested. While the man is in prison, two prostitutes are killed: one inside a phone booth, the other in a park not far from the Lyutaks’ home. The man is released because the killer’s modus operandi and the knife used in the murders are always the same. Miss Heindrich, a police collaborator, senses the truth, but the killer murders her before she can speak. In the end, everything is revealed: Mr. Lyutak had murdered the first victim, while the two prostitutes and Miss Heindrich had been killed by the man’s wife, Marzia Lyutak. By killing the two prostitutes with the same knife her husband had used, she had given Mr. Lyutak an alibi, making the police believe that the killer of the first girl and the killer of the two prostitutes were the same person. Marzia had then also eliminated Miss Heindrich, who had sensed the truth before the police did.