Conventions of the Crime Film

Most sub-genres of crime films have specific conventions which enables the audience to relate to the genre and understand certain parts of the film. Some sub-genres of crime films include, Film Noir, American Gangster, Detective, Spy and Police. 

Typical conventions of;
Film Noir - black and white, voice over (narrative), innuendo, 'The Male Gaze' where the Femme Fatale is a threat to the man and is usually the cause of the murder.

American Gangster - the 'family' act outside the law and see themselves as the authority, slick costumes, all about respect and getting justice or vengeance.

Detective - usually in the countryside, in an upper/middle class manor house, the detective is usually different to everyone else, or not what you'd expect to be a detective (e.g. Miss Marple)

Spy - the spy is always one step ahead of the enemy, a sense of the unknown, anti-hero, often British, the hero always wins.

Police - (British) - lots of action, uniforms, within the law which creates limitations and lack of power, there are usually sharp cuts and uses of montage.

            - (American) - less formal, no uniform and less realistic than British Police films.

British Police: 'Hot Fuzz'

American Police:+ 'Starsky & Hutch'

This clip of 'The Godfather' shows good use of the conventions of 'American Gangster'.