M has been said, by various critics and reviewers, to be based on serial killer Peter Kürten—the "Vampire of Düsseldorf"—whose crimes took place in the 1920s.

M, directed by Fritz Lang in 1931 and written by Lang and Thea von Harbou, tells the story of Hans Beckert (Peter Lorre), a child molester and murderer at large and terrorizing the populace of Berlin. The city's police force, criminal underworld, and citizens all fruitlessly search for the murderer.

Just before the mob can kill Beckert, the police show up to arrest him, along with all the other criminals on the premises. The film ends with a panel of actual judges on the verge of delivering the verdict at Beckert's official trial, only to cut to three grieving mothers waiting in the gallery outside the courtroom.