The Weimar republic was perhaps the single most anxious, mistrusting society in history, and even during the waning years of the depression, with the menace of hyperinflation more or less under control by the end of the 1920s, German war reparations were crippling the economy. With the appointment of dutiful conservative finance pro (and LSE alumnus) Heinrich Brüning as chancellor in 1930, a wave of hugely unpopular policies surrounding the tightening of credit and cessation of any and all salary increases set the stage for the rise of an unstoppably disenchanted and angered populace.

Having captured epic sci-fi fairy tales in both Metropolis and Frau Im Mond (Woman in the Moon), which shot him to the apex of German cinema during the 20s, Fritz Lang and his wife - chief collaborator and scriptwriter, Thea von Harbou - set their sights back to the very earthly criminal underworld they'd previously touched upon in Spione and the first of the Dr. Mabuse films.

The relationship between the very different Lang and von Harbou certainly characterised these films, and ultimately the couple would divorce over von Harbou's affair with Ayi Tendulkar - an Indian Nazi sympathiser (several followers of Ghandi living in Berlin were united with Nazis over their hatred for Britain and adoration of nationalism in any form) - with Lang subsequently leaving the Third Reich for Paris, and then Hollywood. The staunchly nationalist von Harbou stayed behind after the split, going on to direct several films for the Nazi propaganda machine.

Considering what eventually happened, it's hard to watch those Lang-Von Harbou collaborations without seeing the differing visions of the couple silently simmering, battling it out for screen time. The Austrian-born Lang was a very technical cinematic visionary, essentially founding the darkness-riddled tropes of film noir and diving headfirst into pioneering methods (for example, one memorable moment from M sees a camera zoom seemingly impossibly through a window and enter a room, something that Orson Welles would mimic a decade later in Citizen Kane to much laudation). Von Harbou was more overtly a fantasist, often weaving her nationalism into fable-esque Wagnerian mythologies. In hindsight, the pair were perhaps a prophetic microcosm for the society that would succumb to Nazism, and their conflicting moralities and personalities were never more pronounced than in M - a film wherein the overarching theme is a meticulous study of the the unexpected harmonies and discords of human society. Criminals as judges; killer as victim.

M follows the hunt for a child killer, the presence of whom is seeing Berlin pull itself apart. Marking fifty years since the death of Peter Lorre, the BFI will be screening a newly restored version of the film, along with several others featuring the seminal Lorre, including The Maltese Falcon, Josef von Sternburg's Crime And Punishment and Hitchcock's original British production of The Man Who Knew Too Much. Few others that have appeared on screen in the history of film are as memorable as Lorre, yet while he garnered an extensive filmography right up until his death in 1964 - his relocation to Hollywood assured him a fruitful career as the typecast Germanic baddie (and also in the rather more confused role of Japanese detective, Mr. Moto, but that's another essay unto itself) - Lorre would never portray a character quite as challenging, as complex, or as befitting as Hans Beckert, the enigmatic psychopathic child killer at the centre of M.

Even so, there's more to M than Beckert. Despite the depth and draw of Lorre, it's not a character study - it's a melodramatic noir social fable, and as such its cast of characters is comprised of caricatures, all mere players in service of Fritz Lang's greater scheme. While the demonic phantom of Beckert is admittedly a constant presence throughout, and his desperate plea during the film's climactic scene is deservedly ranked amongst cinema's very finest and most harrowing moments, Lorre barely appears in the film's first forty-five minutes or so. M is littered with excellent performances, from the very Charles Bronson-like Friedrich Gnaß's turn as the loveable burglar Franz, to Otto Wernicke's Inspector Karl Lohmann (a character he would later reprise in The Testament of Doctor Mabuse). Lang pulled the very best from all of his assembled cast, and painted an unequalled portrait of a society in the depths of a moral panic.

This restoration can certainly now be thought of as the ultimate one, with the previously bruised and patchy film now crystal clear, and several of the previously missing shots having been finally returned. The sound is perhaps less well done, as Lang's notes clearly stated that several scenes should play out in total silence. Hands tied by the director's wishes, the audio occasionally drops out completely, in jarring contrast with the vintage fuzz and hum that persists in the dialogue scenes. It's only partially distracting, and Lang's requested quiet does lend certain moments a menace that wouldn't persist had street noise and so on remained.

1931 was still pretty early in the history of cinema, and M was Fritz Lang and Thea von Harbou's first film to use sound, yet the film integrates it with the visuals almost as naturally as if they were well versed in the methods that would come into general use later, in the process pioneering a multitude of cinematic crime thriller tropes. The ability to add voice over, and to have characters from one scene talk over footage from elsewhere, lies at the core of how Lang weaves the narrative.

The director fully embraces the new possibilities, with much of the first half of the film taking on a very documentary-like quality as we're treated to phone calls and criminological red tape discussions that cut away to detailed footage of Berlin police procedures and prototype forensics - fingerprints and handwriting being scrutinised in the search for potential clues as to the identity of the killer. Elsewhere, the blanket police raids and drop-of-a-hat accusations across the city chillingly echo its fascist near-future. One group of middle-aged men poring over the Kindermörder in the newspaper eventually erupt into aggressive shouted accusations thrown across the table, that in the years to follow could easily become cries of "juden!", or "traitor!" An entire bierkeller is sealed off as a platoon of uniformed, jackbooted police descend upon the hive of scum and villainy in search of the murderer, and order every single punter to present their papers, or face further questioning downtown. Perhaps most prognostically, the city's criminal gangs, lead by a man known only as Der Schränker ('The Safecracker'), later enlist the services of an all-too willing population of Berlin's homeless in their own search for Beckert. They meticulously organise the homeless into squads, dividing up the city between them, and promising recompense in exchange for the shady business. The hopeless homeless all too willingly oblige, disregarding principals in exchange for a loaf of bread. How better to describe the rise of the Third Reich than as a pop-up army of beggar spies cheaply bought by a gang of thugs?

While the internal battles of the psychopathic Beckert, who is fully aware of, yet utterly disgusted by, his crimes (which we never actually witness on screen), are only hinted at until his climactic declarations at the farcical trial, his amorality is without dispute. Earlier in the film, we see Beckert stop at a shop window, longing after the goods therein with a childlike wonder that echoes an earlier shot of children excitedly peering through a toy shop window. Yet the tender moment is cut short as Beckert spots a lone child reflected behind him, his face suddenly shifting as his manic lust for murder overcomes him once again. Another scene sees Beckert able to control himself, quelling the demonic lust to kill and promptly stopping to knock back a few glasses of cognac to calm his nerves. Later on, Lorre's face becomes once again wide-eyed and childlike, only this time with fear as he realises he's been found out and starts to run.

During the finale, which is most certainly one the best in cinema history, Beckert breaks down, weeping and yelling, decrying the demonic insanity that drives him to kill children. "Who knows what is going on inside me?", he says. "How I must - not want, must!" The criminals that comprise the court are unmoved, never wavering from their persistent wishes for Beckert's execution. Like Beckert, they've succumbed to the demon within, wishing to kill a deranged man, despite any better judgement, and it's the hopeless, chilling message of the film: innocence does not go unpunished. The closing shot leaves us with one of the grieving mothers declaring through her tears, "this won't bring back our children. We, too, should keep a closer watch on our children." In the face of such insanity, what else is there to do?

For more information on the BFI's upcoming Peter Lorre season, head to their website