Your Vice Is a Locked Room and Only I Have the Key (1972)

Once a successful writer, depraved libertine Oliviero can't break out of a persistent creative rut after the death of his adored mother. Nowadays, Oliviero takes great joy in humiliating his beautiful wife Irina and their tolerant maid Brenda in front of his friends. But when someone slits the throat of a young woman, Oliviero becomes the prime suspect, further complicating his already fragile relationship with Irina. And before long, the stealthy killer strikes again. Then, as if murder wasn't enough, Oliviero's seductive niece Floriana enters the equation, and yet another girl meets her end. Who's behind the grisly murders in Oliviero's secluded, blood-spattered villa of vice?