'M' is a 1931 German thriller film directed by Fritz Lang and starring Peter Lorre in his breakthrough role as Hans Beckert, a serial killer of children. An early example of a procedural drama, the film centers on the manhunt for Lorre's character, conducted by both the police and the criminal underworld.

The film was one of the first to use a leitmotif, a technique borrowed from opera, associating a tune with Lorre's character, who whistles the tune "In the Hall of the Mountain King" from Edvard Grieg's Peer Gynt Suite No. 1. Later in the film, the mere sound of the song lets the audience know that he is nearby, off-screen. This association of a musical theme with a particular character or situation is now a film staple, Peter Lorre could not whistle and Lang himself is heard in the film.

'M' premiered in Berlin on 11 May 1931 at the UFA-Palast am Zoo in a version lasting 117 minutes.

More Info: en.m.wikipedia.org