Timeline Goof: The narration states that on February 16, 1929, Al Capone flew straight to Miami, and left Frank Nitti in charge of the Chicago operation. In actuality, Capone went to Miami prior to The Saint Valentine's Day Massacre. Nitti was in St. Louis, not Chicago, on February 16, 1929, getting married in a civil ceremony to second wife Anna Theresa Rango.
Goof: During the narration about The Saint Valentine's Day Massacre, seven hit-men with machine-guns are shown. At the actual event, only two machine-guns were used.
Nitti: (to Moran) You keep takin' over my places, Al ain't gonna leave me in charge long enough to organize my own funeral.
Nitti: (about Capone) He must think I'm some kind of miracle man.
Ness: (to Moran) With your record, they'll convict you on general prinicple.
Lefty: So don't worry about it, Frank, we're doin' the best we can.
Nitti: Oh, I ain't gonna worry...you are. We're gonna have choppers. And if we don't, you're gonna be replaced...permanently.
Nitti: Let me give you a warning, Ness...a lot of punks have tried to buck the Organization. Most of 'em ended up goin' for a swim wearin' cement overshoes. What size you wear, huh?