Peter Lorre
The part of psychologically-unbalanced Hans Beckert was just the third role for Peter Lorre and the one that made him an international sensation whose career wouldn't come to a close until more than thirty years later. Lorre’s diminutive stature, unimposing presence, and babyface made him the ideal choice for a murderer capable of moving about without detection. While Lorre's physical appearance foils our typical picture of a killer and makes him all the more intriguing, it's Lorre's exquisite breakdown in the court scene which catapulted him into stardom.
That stardom worked in Lorre's favor. As Jew fleeing Nazi Germany, Lorre embarked on an illustrious career as a Hollywood character actor, appearing in classics such as Casablanca, The Maltese Falcon, and the first version of Alfred Hitchcock's The Man Who Knew Too Much.
Inge Landgut
Elsie is the first victim of the murderer that the audience gets to know. Briefly. Interestingly, although nearly twenty years Peter Lorre's junior, Elsie had already appeared in four times more movies than Lorre had by the time she played his victim. Later on in her career, she would work as a voice actress dubbing English-language film and television into German. This was a common practice, as subtitled movies rarely ever played in Germany. Her most prominent role in this gig was voicing Wilma in the German-dubbed Flintstones.
Otto Wernicke
As the detective obsessed with stopping the child murderer terrorizing the city, Wernicke turned in one of his earliest performances as well. Wernicke would stay in Germany during the war and go on to have a long career both during the war and well after.
Gustaf Gründgens
By far the most notorious actor associated with the film is Gründgens, who played the underworld leader who joins the police in hunting down the killer because he was becoming bad for the business of crime. During Nazi rule, Gründgens gained prestigious appointments thanks to connections with Herman Göring and Joseph Goebbels. He became one of the entertainment industry's key Nazi collaborators, joining Gottbegnadeten-Liste of artists considered crucial to spreading Nazi culture. His definitive interpretation of Mephistopheles in productions of Faust was chronicled first in a book and later an award-winning film titled Mephisto, where he was portrayed by Klaus Maria Brandauer.
Georg John
Further underlining the importance of casting Peter Lorre in the role of the killer is the fact that ultimately he is identified by a person incapable of being distracted by his looks. Georg John plays the blind balloon vendor whose sense of hearing is the cause of Beckert’s downfall, thanks to the latter's habit of whistling the same an tune in off-key manner whenever he is on the prowl for his next victim. A decade after fingering Peter Lorre as the killer, John would die in the Lodz Ghetto, deprived of his career, his health, his future and his life by the Nazis because he was both Polish and Jewish.
Carl Balhaus
Balhaus may be all but unknown by even the most rabid of classic film fans, but he does hold the distinction of making what is, arguably perhaps, the most significant use of a piece of chalk in movie history. Balhaus is the fellow who writes an “M” on his palm, pretends to trip and bump into Beckert and leave the incriminating mark of identification on the back of Beckert’s coat.
