Other mistake: When Nitti (Billy Drago) kills Oscar in the elevator, not only is there not nearly enough time for him to write "Touchables" on the wall, but the writing looks like it was done with the aid of a ruler. If he had actually written it in the minute it took the elevator to reach the bottom floor, it would be smeared all over the place. (01:06:50)
Other mistake: When the agent is shot in the freight elevator he is shot point-blank in the head. However, when Ness finds him there's not a drop of blood on his clothing, or a hole in his head.
Answer: It's about 50% truth and 50% fiction. Ness, Al Capone, and Frank Nitty are real, of course, but the characters played by Connery, Garcia, and Smith are fictional. Ness started out with 50 candidates for his 'Untouchables' force. This was whittled down to 15 finalists and from that he selected 9 agents (none of which has the same name as the characters played by Connery, Garcia, and Smith). It's true that Capone was convicted for tax evasion. He was sentenced to 11 years in prison, but received an early release because he was in the last stages of syphilis. He died shortly after being released from prison.
raywest ★
Capone lived for 8 years upon his release from prison. The 8 years being slightly longer than the actual prison time he served, which was just over 7 years. He died, having the mental capabilities of a 12-year-old.