Peter Lorre owed RKO two days on his contract and was given this role with few scenes and few lines. He received top billing largely because his was the most recognizable name among the film's principal cast.
This film or The Maltese Falcon (1941) is often cited by film historians as the "first film noir", while M (1931) is considered an important precursor to film noir. Peter Lorre stars in all three films, and Elisha Cook Jr. is in the two American films.
This film was not a success at the box office, resulting in a loss to RKO of $56,000 (nearly $1.2M in 2022) according to studio records.
When John is convincing Mary that the same man committed both murders, the image in the background is the Washington Square Arch / NYC's Washington Square Park.