Perfect Witness (1989)

This is the story of Sam Paxton (Aidan Quinn), who witnesses a mob killing, and rather than testify, he goes to prison. When released, he decides to finally testify, even though it means that he and his family will have to go into the Witness Protection Program, thereby disrupting their lives. However, an unexpected courtroom maneuver by District Attorney James Falcon (Brian Dennehy) changes the outcome for this man.