There is this really disturbing movie I've been trying to find recently, where a guy apparently in a demential state, watches a movie on theater where there is a "mother", who always calls a man's name and brainwashes him into obeying her or something. Her voice was from an old woman, pretty creepy and annoying, much like the voice of the medium of Poltergeist. The guy seems to be getting controlled by this "mother" from the movie.
Later, there are two girls that go watch the same movie on the theater with that guy, and suddenly the guy starts killing everyone inside with a gun. The girls manage to escape but one remains inside the theater, hidden. The other goes to get help from police.
The scene that mostly comes to mind is the girl hidden in the toilet watching the killer walking from under the door, while he was searching for her.
In the end both girls survive I think, and the police manages to catch the killer in the theater.
The movie is from around the 80s I believe. I watched it in television. Can't remember anything else.