Revealing mistake: When Sean Penn is in the funeral home looking at his daughter's body, when he lays the dress over her the rise and fall of the very alive actress' chest as she breathes.
Factual error: In the scene at the beginning of the movie as the 3 youths walk up the street, you can see current MA license plates, although the action should have taken place many years earlier.
Visible crew/equipment: Before we first see the marching band, and Kevin Bacon finds out what his daughter's name is, there is a shot looking at him in his car and he drives off screen. As the car goes out of the shot to the left, check out the reflection of the camera man in the rear driver's side window.
Continuity mistake: In the scene where Kevin Bacon and Laurence Fishburne go to Tim Robbins' house to speak to him about being in the bar on the night of the murder, they all walk down the street together, as Dave is walking his son to school. In one shot, following the men from behind, it shows them walking past a red brick building, then a blue cape cod style building. When they are about halfway past this blue building, it cuts to a shot taken from in front of them (showing their faces), in which we can see them walking past the red brick building and then the blue building again.
Continuity mistake: When Penn is drinking whiskey, he puts the bottle on the table, with no hull, later it has a hull and then it's again with no hull.
Other mistake: On the tape of the 911 call regarding the murder a boy says "They want to know her name" to a supposed accomplice. However one of the two boys who are accused of the phone call and murder at the end of the film is deaf, and the two boys communicate with sign language - the boy who could talk would never say anything to the other.
Factual error: In the scene where young Dave Boyle is being driven away by the pedophiles, he looks out the rear window of their car and locks eyes with his friends standing in front of the street hockey goal, which is in the middle of the street. How did the car get past it?
Factual error: In the first scene the boys are playing street hockey using sticks that have plastic blades made with holes in them for better aerodynamics. These blades were not available in the mid-70's. We know this scene is taking place in the mid-70's because Dave tells his son he was in high school from 1978-82. The scene takes place when Dave is 11, too young to have been in high school.
Visible crew/equipment: When Sean Penn is picking out headstones, you can see the tracks and the wheels of the dolly for the camera being reflected in the headstone.