M represents Fritz Lang's transition to sound, but his miserly use of it illustrates why galloping music and sudden, jump-out-of-your-seat aural effects have blunted the impact of so many suspense films. Lang's seemingly innocuous brushstrokes -- the playful sound of a man whistling, a balloon swaying slightly in midair, a child's eager face -- are really a prelude to the kid's murder. The mundane details are vital from the pathetic killer's point of view: He sweatily clutches his surrounding sensory debris to block out the crime.
M pissed off Nazi officials, ostensibly because of its morally ambivalent view of Lorre's character, but more likely because it casts a harsh glance at the mechanics of mob justice. If a popular filmmaker were willing to suggest that a lynch mob might be just as reprehensible as a lone pathological killer, he surely wouldn't be too eager to join the cultural disparagement of Jews, leftists, gypsies, homosexuals, and other undesirables. Indeed, after Lang's next movie, 1933's The Last Will of Dr. Mabuse, showed the villains spouting Nazi propaganda, his work was banned and The Third Reich demanded he make movies for their cause. Lang fled the country without his personal belongings or his wife, who had become a Nazi screenwriter.
Still, you wouldn't need to know anything about its historical context to appreciate that M is one of the eeriest psycho-killer movies ever made, all the more disquieting because it reverses the relationship between society and the criminal who preys on it. By the time a delirious Peter Lorre is corraled by the seething masses, you'll also feel a bit disoriented at the inability to make your sympathy stick with any one side.