This film is an absolute masterpiece, and check out Peter Lorre's unbelievable performance.
From Time Out Film Guide
Lang's first sound film was based on the real-life manhunt for the Düsseldorf child-murderer (an extraordinary performance by Peter Lorre). A radical, analytical film that entertains many of Lang's fascinations: innovative use of sound; the detail of police procedure; the parallels drawn between organised police behaviour and the underworld... a construction which carries Lang's own view of the arbitrariness of the Law. A subversive film, or more simply a movie brimming over with the ferment of Lang's imagination at its height? You choose