The first widely-released "mockumentary."
One hundred San Quentin prisoners were paid a small fee to work on the film during the prison sequences. The regular cast and crew were stamped each day with a special ink that glowed under ultra-violet light so the guards could tell who was allowed to leave the prison grounds at the end of the day.
Woody Allen later said he was not nervous about his first day but was so excited about shooting on location in San Quentin prison that he cut his nose shaving that morning. The mishap can be seen in the prison scene in the movie. He and his team found the inmates there to be very friendly and cooperative. The prison authorities also eagerly welcomed the production but issued a warning: cast and crew were always to be accompanied by guards and if taken hostage, the gates would not be opened to secure their release.
The original ending of Virgil dying in a hail of bullets would have been followed by a brief humorous scene at his funeral when his wife hears him whisper from below ground, "Get me out."