Continuity mistake: During the meal, when Al Capone says he loves baseball, the man on the right holds a cigar with his hand. A shot later, from another angle, the cigar is on a plate and he is clapping.
Continuity mistake: A man enters Ness's office and throws a manila envelope on top of a sheet of paper. In the close-up, the paper transforms into a folded newspaper and the envelope appears perfectly lined on it.
Continuity mistake: In the elevator murder scene, in one shot there's not much blood on the wall, but in the very next shot there's much more.
Continuity mistake: In the final court case, as Eliot Ness escorts out Nitti, Ness's wife watches them leave and is wearing a brown and cream hat, with a brown jacket. When the case finally resumes and the guilt plea is changed, Ness's wife is again shown, except this time she's wearing a light blue hat with dark blue ribbon, a blue jacket, with a floral green and blue blouse.
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.