I'm looking for a movie with a plot similar to an Experiment in terror. I can only recall the final scene. A woman watcher his friend and an intruder fighting after the friend subdues the intruder he removes a tape recorder from the man with the voice he used over the telephone. After a while we realize, by the friends speech that he's in fact the villain and the intruder was a policeman. I would apreciate an answer quickly thanks.