At one point Betty Anne Waters Hilary Swank tells Kenny Sam Rockwell that it's a good thing Massachusetts doesn't have the death penalty or he could already be dead. This however is incorrect. Massachusetts still had the death penalty in 1983, when Kenny was convicted. It was abolished the following year in 1984.
In various scenes where Hilary Swank and Sam Rockwell's characters are meeting in the jail, the Sprite that Hilary drinks from has the new logo from 2005 consisting of two yellow and green "halves" forming an "S" lemon/lime design. This logo had not yet been created during the implied times of these scenes.
While Swank and Rockwell are talking in the prison visiting room, the voices of their characters remain clear, unobstructed, and loud, despite camera angles changing to long shots, through windows, and from behind at a distance. Normally in editing, there is an attempt to mimic how the sound would be received by the viewer if they were in the camera's position, such as when music playing on a car stereo decreases and is muffled when heard from someone outside versus inside the car.