Answer:
In the movie 'M,' the serial killer Hans Beckert is revealed by the criminal underworld, not the authorities, and is marked with the letter 'M.'
Step-by-step explanation:
In the movie 'M' by Fritz Lang, the identity of the serial killer Hans Beckert is ultimately revealed not by the authorities but by the criminal underworld of the city. Beckert, portrayed by actor Peter Lorre, is marked with the letter 'M' by the other criminals as a means of identification so they can capture him. The film is a significant work of the German cinema and showcases the director's ingenuity and ability to delve into the psychology of a killer, while also exploring the themes of justice and vigilantism.