- Breakout Character: Otto Wernicke's Kommissar Lohmann was so popular with viewers that Lang brought him back for Das Testament des Doktor Mabuse one year later.
- Fridge Horror: Considering what mental hospitals were like in the 1930s, the death penalty might be kinder for poor Hans. He's pretty screwed either way.
- Worse still, remember that the Nazis only assumed power two years after this film was released. How do you think they are going to treat a mentally-ill Jew?
- Harsher in Hindsight: Or at least, ironic in hindsight. Der Schranker, the faux-Nazi head of Berlin's underworld, is played by Gustaf Grundgens, who became director of the Prussian National Theater under the Nazis and a favorite of Hermann Goering.
- Misaimed Fandom: The Nazis. They even took Hans speech at the end to "prove" that Jews were all evil. Because Peter Lorre was Jewish, and he played a Serial Killer, that means that all Jews are serial killers, right? It's doubly ironic from the lawyer's equally-impassioned speech in which he states, "No one has the right to kill a man who is incapable of responsibility for his actions! Not even the state!"
- Everyone Is Jesus in Purgatory: Very much like in Lang's other famous work, the Nazis were completely oblivious the blatant Take That made against them in the film - or, for that matter, the film's intentionally Grey and Gray Morality. Joseph Goebbels, who was directly mocked in the movie as der Schränker, said that it was "fabulous! Against this 'humanitarianism' tripe. For the death sentence!" It took them the emigration of Lang to finally see the movie for what it was.
- Moral Event Horizon: Subverted, in that you'd expect the act of murdering little girls to automatically lose the audience's sympathy, and yet...
- The Woobie: Only Peter Lorre could make a child killer into a Woobie.