Crime Cliches

Most of the essential,indispensable cliches in films about crime - the police are as bad as the gangsters, just try find an LA cop who's not on the take-were established many, many years ago, and films that ignore them rarely succeed in the box office.
Crime movies almost always have a rat, and sometimes several. Gangsters have a hard time identifying the rat in the crew, even though the rat is always the newest and best looking member of the gang, and never seems to belong to the same ethnic group as everyone else in the gang.

Gangster movies often include a scene in a restaurant or nightclub where somebody says the wrong thing to the wrong guy and later regrets it.
In crime movies, there is usually one straight arrow whom the gangsters respect because he is not completely crooked like them.
The crime genre must also be looked at from the perspective of the cops. For a crime film to work, there must be a wizened, cynical cop who is close to retirement and has seen it all. There must be a young cop who just got married, and who will almost certainly die. There must be a full-dress funeral service, preferably in the rain.

Finally gangster movies would not be gangster movies without the crucial scene in the hospital where a good looking young cop comes on duty to replace the cop who is guarding an important witness, and then turns out to be a hit man.