These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Al Capone's Theme. The second half plays during the scene where a jubilant Al Capone gets word that Eliot Ness' sting operation was a fiasco; there's even a very jarring "wah-wah" horn section in it, as if Capone is mocking Ness.
Complete Monster: Frank Nitti, 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, slaughtering two policemen on The Untouchables 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 attempts 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.