The film is inspired by the murder of voting rights activists James Chaney, Michael Schwerner, and Andrew Goodman by the Ku Klux Klan.
In a review for Radio Times, former BBC film critic Barry Norman described the film's opening as "pure cinema, something no other medium could do so effectively."
The coroner determined that James Chaney and Michael Schwerner were dead when they were buried. Traces of red clay in Andrew Goodman's lungs and fists indicated that he was buried alive.
Gene Hackman decided that he would no longer make violent films after seeing a brief, violent clip of his performance in this film (taken out of context, in his eyes) at the 1989 Oscars. That stance prevented him from accepting a job as director of Il silenzio degli innocenti (1991) and almost cost him the Sheriff role in Gli spietati (1992), which he reluctantly accepted after Clint Eastwood convinced him. That role that earned great acclaim, and his second Oscar.
The methods used by the FBI later in the film to fight the Mississippi White Knights of the Ku Klux Klan were part of the infamous Counterintelligence Program (COINTELPRO) under J. Edgar Hoover, which started in 1956 and ended in 1971.