The role of Rosa Nicolosi was considerably expanded from her novel counterpart to give more prominence to star Claudia Cardinale.
The plot is loosely based on the 1947 murder of Sicilian trade unionist Accursio Miraglia by the Cosa Nostra.
American actors Lee J. Cobb and Nehemiah Persoff were both dubbed in the original Italian version, Cobb by Corrado Gaipa and Persoff by Arturo Dominici.
Protagonist Franco Nero was born in Emilia-Romagna, more specifically in the Comune of Parma, just like the character of Captain Bellodi he plays in the movie.
The dynamics of Colasberna's murder are greatly different from the novel's depiction, in which he runs to board a bus and is killed in the process by an unknown rifleman. Instead, in the film he is driving a truck when he is shot dead but is able to open the door and throw himself out. The occupants of said bus only find the corpse on the roadside.