Sequel

Apparently a sequel was made called 'Three Strangers'. The movie's available on Amazon so I'll probably check it out. Here's what's said about it in the Trivia section:

When Warner Brothers saw how successful the film was, it decided to produce a sequel. Director John Huston had written a script for the sequel, to be titled "Three Strangers". The film was supposed to contain many of the primary characters from this film, specifically Sam Spade. Before the film reached production, however, Dashiell Hammett informed Warner Brothers that he owned the rights to the characters, and even though the studio had purchased the rights to the novel, it did not own the rights to the characters. Three Strangers (1946) was eventually filmed with different characters. Peter Lorre and Sydney Greenstreet appeared in both "The Maltese Falcon" and "Three Strangers".