Visible crew/equipment: Towards the end of the film when Billy runs at the top of the screen towards the exit of the jail, you can see the film crew at the bottom of the screen.
Visible crew/equipment: When Billy bribes the main guard, who then drags him up to his office, the camera pulls back dramatically to reveal a crew member tracking them with a boom mic.
Visible crew/equipment: When Billy's girlfriend, Susan, visits him at the insane asylum section of the prison, just before Susan enters there is a reflection of a crew member on the left side of the screen giving the shot a ghostlike image. (01:35:15)
Visible crew/equipment: Billy is going crazy, kicking a guy on the ground. The camera follows the action. In one scene the shadow of the operator is blatant on the left side. (01:37:00)
Visible crew/equipment: Billy runs into a bus, narrowly missing a door closing. He looks out the window and smiles. The head of a crew member is visible reflected in the glass.
Chosen answer: Billy's plan was to bribe a guard to help him escape, using the money his girlfriend had smuggled to him. That plan failed, and he was almost raped by a sadistic guard. When Billy accidentally killed him, he used that as an unexpected opportunity to disguise himself in a guard uniform and walked out the front door. If he had been caught, he did not have an alternate plan and would have been severely punished, probably even executed.
raywest ★