The scene where three different characters take turns breaking through the concrete floor of their cell is filmed in a single, nearly four minute long, shot.
La Sante prison was replicated right down to the smallest details, thanks to the help of the three actual members of the escape whom Jacques Becker hired to serve as production consultants.
The film was completed according to the director's wishes after his death, but producer Serge Silberman had it reduced from the initial 140-minute version by about 24 minutes to enhance its commercial possibilities. The missing footage remains lost.