Circuito chiuso

An audience is watching a western in a cinema. Then suddenly a gunshot is heard and an man dies in his chair shot. The police immediately starts an investigation and nobody is to leave the theater. The killer has to be in the building so it has to be just a matter of time that the killer will be found. But the strange thing is they cannot find him or any weapon. Further investigation reveals some strange facts and when they reenact the situation another man is killed in the same chair. (imdb)