Tenebre (1982)
While promoting his latest murder mystery in Rome, American author Peter Neal (Anthony Franciosa) becomes embroiled in a real-life murder mystery involving crimes committed by a fiend who’s dangerously obsessed with his novels. Tenebre is more giallo than straight-up horror (as are several of the other films on this list), but the mystery is pleasingly twisted and the death scenes are as gory as you’d expect—plus, Franciosa’s co-stars include Nicolodi as Peter’s peppy assistant and the great John Saxon as his even peppier, jaunty-hat-wearing agent.