This film's shooting schedule went over-time and consequently actor Robert Redford had to start work on his directorial debut Ordinary People (1980) with very little time at all between projects.
The warden impersonating a prisoner story element was fictionalized and was not derived from Thomas O. Murton's experiences. It has been suggested though that this plot device was inspired by Sing Sing Prison Warden Thomas Mott Osborne who in 1913 under an assumed name had had himself committed to New York State's Auburn State Penitentiary.
This film was made and released about eleven years after its source book "Accomplices to the Crime: The Arkansas Prison Scandal" by Thomas O. Murton and Joe Hyams was first published in 1969. The film is a fictionalized version of this book and was also based on Murton's true life prison system experiences. The film was made and released about twelve to thirteen years after the events of the Arkansas Prison Scandal had taken place around 1967-1968.
After leaving the prison board meeting, while speaking with Lillian Gray in the Hilton Inn parking lot, Brubaker claims to have locked his keys in the car. Lillian Gray then opens an unlocked passenger-side door (humiliating Brubaker).
At the conclusion of a previous scene, when Brubaker is leaving for the prison board meeting, an angry Dickie Coombes slammed his hand down on the passenger side door, locking it (the camera is focused on this action).