Alternative Character Interpretation: Possibly overlapping with Fridge Brilliance; Capone's lawyer, at the end, immediately enters a plea of guilty as soon as the judge orders the bribed jury swapped out for another one. The lawyer does this without Capone's consent which, as noted on this wiki and elsewhere, is grounds for an immediate mistrial in real life. Anyone ever consider that said attorney knew this and pulled the stunt as a Hail Mary to get Capone off once he knew it was otherwise all over?
Complete Monster: Frank Nitti is presented as a Psycho for Hire for Al Capone. Introduced early on as Capone's main enforcer and hitman, Nitti is seen bombing a restaurant with a little girl inside, not caring that she's killed as well. Through the film, Nitti handles Capone's wetwork, ruthlessly murdering anyone in his way with barely disguised relish, continuing to eat his meal even as the man right next to him is having his brains bashed out by Capone, slaughtering both Oscar Wallace and the Capone man apprehended by the squad and writing "touchable" on the wall in their blood, and later gunning down tough Irish cop Malone. He threatens Elliot Ness's family if he won't drop his case. Nitti later tries to rub his own status as untouchable in Ness's face, even taunting him that Malone "died screaming like a stuck Irish pig," which finally makes even the composed Ness snap (leading Ness to throw Nitti off the roof, with Ness taunting Nitti as he falls screaming to his death).
Similarly, Austrian-born actor John Banner appeared on the TV show as a Bavarian brewmeister, who is later confronted by a fellow brewmeister - whose brewery was rushed by the police - to see what he knows about any of it. He knows nussink! NUSSINK!
Toward the end of the bridge scene, Ness throws a frag grenade at one of the gangsters, which then explodes. Even on a first viewing, it's apparent that the grenade itself does not blow up, but rather a separate charge buried directly behind it.
The green screen effects during Nitti's death scene are pretty noticeable as well.