Historically inaccurate
The part where Ness takes a smoke break during the Capone trial, encountering Frank Nitti in the hallway who happens to have a matchbook with Ness's best friend's street address written on it, culminating into a rooftop chase where Ness eventually tosses Nitti over the side of the building to his death.....
in truth life, Ness threw him into the lake at an alligator farm.