Killer Reserved Nine Seats, The (1974)

aka: L' Assassino Ha Riservato Nove Poltrone

Nine people are lured to an old theater to spend a weekend for a stage rehearsal. Soon, they discover they are trapped inside and a mystery killer starts murdering in inventive and gruesome ways. With Rossana Schiaffino, Chris Avram, Lucretia Love, Paola Senatore, Andrea Scotti, Eva Cemerys, Janet Agren and Howard Ross. (Uncut)