Mystery films are primarily concerned with solving crimes, most often murders. Detectives are generally heavily featured, whether they are of the private variety or those who work for a police force of some kind. This central character frequently investigates an unsolved crime and unmasks the perpitrator. These films in general conceal the identity of the guilty party almost right up to the end, although some of them will allow the viewer to identify the culprit right from the start and then watch as the police or detective tries to trip him up.