M is for Murder, or Mörder, the chalked letter pressed on the shoulder of a notorious child-killer in Berlin by a member of an organised criminal underground – a secret sign to identify the psychopath and kill him. This is so that the police can call off their own city-wide manhunt, which is seriously inconveniencing the criminal classes.
Peter Lorre plays the porcine, pop-eyed serial killer Hans Beckert, speaking German with a rasping, querulous shout. Otto Wernicke plays pudgy police inspector Lohmann, and Gustaf Gründgens is Schränker, the crime overlord who will finally sit in judgment on Beckert, presiding over something between a kangaroo court and a revolutionary tribunal. Lang depicts the paranoia and feverish atmosphere that gives birth to the dual investigation from the cops and the criminals. Lohmann has a determined, forensic technique, analysing the handwriting on Beckert's jeering letter to the press, and the woodgrain of the table the paper appears to have pressed on.
Meanwhile, a hidden army of crooks and thieves pass on their own tips, and a blind peddler crucially recognises the tune Beckert whistles. It is a cousin to the early Hitchcock of The Lodger. What is fascinating is how Lang fetishises smoking: everyone has huge cigars, bulbous pipes and cigarettes in holders. It is as if smoke is the endless industrial byproduct of the city's folly, greed and shame.