M (1931 film)

M is a 1931 German mystery thriller directed by Fritz Lang, from a screenplay Lang wrote with his wife Thea von Harbou, starring Peter Lorre in his third screen role as Hans Beckert, a serial killer who targets children. Lang's first sound film, it follows both the city's police force and its criminal underworld as each races to track down the murderer, and is regarded as an early example of the procedural drama. Noted for cinematic innovations including long tracking shots and a recurring musical leitmotif whistled by Lorre's character, it is widely considered one of the greatest films ever made and an important influence on later crime and thriller fiction; Lang himself called it his magnum opus.