The Killer Reserved Nine Seats
L'assassino ha riservato nove poltrone (original)
A rich man gathers together friends and relatives at the abandoned theatre he owns, but the party isn't fun for long since apparently one of them is a murderer.
Starring Chris Avram, Rosanna Schiaffino, Eva Czemerys, Lucretia Love, Paola Senatore, Gaetano Russo, Eduardo Filipone, Howard Ross, Janet Ågren, Andrea Scotti
Watch "The Killer Reserved Nine Seats" on Amazon released in 1974. It's a mystery and horror movie, and has a rating of 5.7 out of 10 from Imdb which is fairly okay for this kind of movie, and is currently only available for purchase or rent.