Men of this era almost never wore their Hats inside of a building. It was considered rude and disrespectful to do so.
Milo Gibson, who plays Al Capone, is the sixth son of Mel Gibson.
The actor Mark Ralston, who plays Dion O'Bannion was 61 at the time the movie was made. The real Dion O'Banion was assassinated at 32 reportedly by Frankie Yale, John Scalise and Albert Anselmi.
The politician on the stairs running for office is Tommy Gunn, long-time adult movie star.
Jamie Lynne-Sigler and Jason Patric played in the same episode in the show Entourage, but had no scenes together.