• 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!"
  • 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.