The Testament of Dr. Mabuse (1933)
Alternate-language version of
Otto Wernicke as Kriminalkomissar Lohmann appears in both.
The doctor sings the melody from "Walkuere" because he misses the first act, like Commissioner Lohmann in "Testament". The (uncredited) actor looks exactly like Lohmann.
The final shot in Mabuse is referenced in the penultimate shot of The Godfather.
Both movies feature a scene where a couple floods a room with water in order to escape from it
The German text recited by Hans during his hotel room performance is taken directly from the journal of Dr. Mabuse read by Prof. Baum in his study.
During doctor Busé's lecture he shows a photograph of Dr. Mabuse
The transformation scene in the jail cell is an homage to a nearly identical scene in The Testament of Dr. Mabuse.
movie poster shown
excerpt in movie
Criminal genius is incarcerated in a mental institution but his criminal plans are realized by others