The Sunday Woman (1975) [Blu-ray]

An odious architect is beaten to death and a high society wife (Jacqueline Bisset, Day for Night) and her gay friend (Jean-Louis Trintignant, The Conformist) are the key suspects with a discarded letter implicating them in the crime. Commissioner Santamaria (Marcello Mastroianni, Fellini's 8 ½) is assigned to the case and tries to uncover the murder suspect in upper-class Turin.