Eyes Behind the Wall (1977)

Ivano is a wheelchair-bound man with some strange perversions. He gets his sexual kicks by spying on Arturo, their tenant in the apartment next-door and forcing his sexy accomplice Olga to watch as well. To increase his perverse thrill, Ivano persuades Olga to seduce Arturo and to have sex him as he watches. Unfortunately for all involved, the sex game starts to get very deadly.