M

M (1931)
IMDB #57 [http://www.imdb.com/title/tt0022100/]

The Gist:
Peter Lorre is a murderer, a child murder, a child rapist/murderer, generally not a nice dude. Strangely he doesn't get a lot of screen time as the film focuses more on how his actions provoke those around him, creates a panic that stirs the city, and starts a manic man hunt from police and criminals alike. At the end you have an odd "trial" run by the criminal underground which becomes more of a philosophical forum for how society should punish criminals like Lorre's character. Due process or righteous destruction?