Other mistake: In the film, the character of Sister Helen is played by Susan Sarandon. Midway through the movie, there is a scene where several people are congregated outside the building where Poncelet's appeals are being held. Sister Helen is talking to her laywer friend, who, at the end of their conversation says, "OK, see you later, Susan."
Factual error: Almost at the end of the film, Poncelet is marched to the death chamber, with Prejean's hand on his shoulder. They are led past an open door - which leads to the viewing room, where the witnesses will congregate. Some of them are already in the room. This is nonsense - it is inviting a bereaved relative to attack the condemned man. In fact the corridor to the death chamber goes nowhere near the witnesses' area, and Prejean would have had to have been escorted back through two guarded doors to reach it.
Continuity mistake: When Sister Helen is being pulled over for speeding, in the view through the rear view mirror, the cop car behind her is driving on the left side of the road, with the police officer driving in the right front seat, on a straight road with a solid center line. In the next shot, both cars are on the right side of the road, with the police officer sitting in the left front seat, on a curvy road with a dashed center line.
Visible crew/equipment: When Sister Helen and Mr. Delacroix are speaking in his living room, as the camera is panning out in the living room at the conclusion of their discussion, a crew member wanders into the background outside the window and then quickly runs out.