When Mrs. Pell is in her living room watching the television game show 'To Tell the Truth', it appears to be well after dark outside. From 1959 until 1966, this half-hour program aired on CBS at 7:30 PM ET/6:30PM CT. During the summertime in Mississippi (when the film is set), it would still have been broad daylight outside while this program was being telecast.
At the end of the movie, when people are gathered around the tomb marked 1964 and the black woman is singing, one blonde child is wearing ceramic brackets. On the time depicted that type of orthodontic technology was not developed yet.
When Baines is trying to escape, Anderson blocks him at the doorway holding up a set of handcuffs with the thumb and forefinger of his left hand. In the next closer shot, he is dangling the handcuffs from his index finger.
When Agents Ward and Anderson are fighting outside the hospital where Mrs. Pell is after being beaten by her husband, Ward pulls a gun on Anderson. We hear Ward cock his revolver. In a subsequent shot, while Ward still has his gun pointed at Anderson, we can see the hammer has not been pulled back as the sound effect would have indicated.
When the Choctaw man leads the FBI agents through the swamp, the water level never goes much deeper than their knees. But his clothes are suddenly wet above his waist, most likely from multiple takes in different water levels.
The movie is set in "Jessup County", Mississippi. The events on which the film is based occurred in Neshoba County, but it is likely that the producers deliberately altered the setting to dispel perceptions that the film is a true documentary.