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 "Cosa Nostra", the Italian criminal syndicate in Sicily, which is also known as "The Mafia", translates into the English language as "Our Thing". Director Terence Young commented that "actually, the word 'Mafia' is never used by Italians because it is a word used only by outsiders. Italians talk about it as the Cosa Nostra, and we show how it came into being". Young stated that the terms "Mafia" and "Cosa Nostra" were both used on the movie's sound track. Moreover, Young maintained at the time of the film's launch that Joseph Valachi was "the only time when an insider in the Cosa Nostra broke his oath and told his story".
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".