In return for using the penitentiary grounds of the Sing Sing Correctional Facility, the production made a large contribution to the prison's recreation fund.
Producer Dino De Laurentiis acquired the screen rights to Peter Maas' novel in 1969. As soon as the movie was announced, De Laurentiis said that he started getting telephone calls from unidentified people 'inviting' him to drop the project. Undaunted, he pressed on.
The film's opening prologue, a quote from Senator Robert F. Kennedy, states, "Crime is a question of criminals. It is not a matter of race, color or religion - Robert Kennedy when Attorney General of the United States". Bobby Kennedy was relentless about pursuing the Mafia.
Due to a special agreement with the Sing Sing Prison, about 100 convicts worked as extras and background actors.