Fritz Lang's most famous film 'M - Eine Stadt sucht einen Mörder' from 1931 uses the soundtrack from a famous theatre piece - which one?

Explanation

Fritz Lang is one of the 'grand old men' of German language film. He made himself noticed in the 1920s with the film 'Metropolis', which has later inspired the whole science fiction-genre. He also directed big films in the 1920s, including the classic 'M - Eine Stadt sucht einen Mörder' from 1931, which uses the soundtrack from 'Peer Gynt'. Later, he went to Hollywood and enjoyed tremendous success with e.g. 'Fury' from 1936, starring Spencer Tracy.