M is a 1931 German mystery thriller film directed by Fritz Lang and starring Peter Lorre as Hans Beckert, a serial killer who targets children, in his third screen role. Both Lang’s first sound film and an early example of a procedural drama,[2] M centres on the efforts of both a city’s police force and its criminal syndicates to apprehend a serial child-murderer.

https://en.wikipedia.org/wiki/M_(1931_film)