Louise Brooks is in studio records/casting call lists playing "Bess" in this movie, but she and her character, did not appear.
Edward Woods was originally hired for the lead role of Tom Powers and James Cagney was hired to play Matt Doyle, his friend. However, once director William A. Wellman got to know both of them and saw Cagney in rehearsals, he realized that Cagney would be far more effective in the star role than Woods, so he switched them.
James Cagney based his performance on Chicago gangster Dean O'Bannion, and two New York City hoodlums he had known as a youth.
According to James Cagney's autobiography, Mae Clarke's ex-husband, Lew Brice, enjoyed the "grapefruit scene" so much that he went to the movie theater everyday just to watch that scene only and leave.
At about half an hour into the film, there is a sign indicating a showing of the Duke Ellington film, Black and Tan. Since "The Public Enemy" has much to do with prohibition, this is a clever pun by the filmmakers, as a black and tan is also a common mixed drink (typically stout and ale, hence its name).
Because of the famous grapefruit scene, for years afterward when dining in restaurants, fellow patrons would send grapefruit to actor James Cagney, which - almost invariably - James Cagney would happily eat.
Further connection to the O'Banion reference is the bad guys in the film are led by "Schemer Burns" which is an obvious reference to the real life "Schemer Drucci", who was part of the North Side Gang led by O'Banion.
In an early scene, set in 1914, a piano can be heard in the background, as someone slowly plays through Scott Joplin's "Maple Leaf Rag".
Ranked #8 on the American Film Institute's list of the 10 greatest films in the genre "Gangster" in June 2008.
Several versions exist of the origin of the notorious grapefruit scene, but the most plausible is the one on which James Cagney and Mae Clarke agree: The scene, they explained, was actually staged as a practical joke at the expense of the film crew, just to see their stunned reactions. There was never any intention of ever using the shot in the completed film. Director Wellman, however, eventually decided to keep the shot, and use it in the film's final release print.
The infamous grapefruit scene caused women's groups around America to protest the on-screen abuse of Mae Clarke.
The machine gun attack on Cagney and his best friend Matt Doyle actually used real machine gun bullets. An expert with the gun stood 15 to 20 feet away from the target, and when Cagney's face disappeared behind the corner of the wall, he opened fire and created that tight circle of machine gun bullets.
The movie "Mob Boss" is probably based on the wildly popular "Little Caeser," starring 'Edward G. Robinson'. One of the stars, George Raft, actually was an associate of Owney Madden.
The scene where Tom shoots the horse that threw and killed Sam "Nails" Nathan in a riding accident was based on an actual incident. In 1924, Sam "Nails" Morton, a member of Dion O'Banion's gang, was thrown from his horse and killed while riding in Chicago's Lincoln Park. Other members of the gang, led by Louis "Two Gun" Alteri, kidnapped the horse, took it to the spot where the accident occurred, and shot it dead. Source: Carl Sifakis, "Encyclopedia Of American Crime."