The amount of shaving cream on Mayor Quintana's face when he is at the barbers.
The film shows Giuliano trying to stop the massacre at Portella della Ginestre (blamed in the film on Terranova, who was one of the few of Giuliano's band who it's definitely known did NOT fire a single shot on that day). In reality Giuliano always accepted full responsibility for the massacre and expressed no sorrow for the victims.
Giuliano never hijacked any troop trains or crucified any priests.
In the film Giuliano is seen smuggling grain to give to the starving. In reality he sold it on the black market.
When Don Masino goes to meet Giuliano the camera crew are clearly visible reflected in the open door of the car.