Dario Argento's usual collaborator Ennio Morricone scored the film, but had a major argument with Argento over some tracks Argento didn't want in it. As a result, the director and Morricone would not work together again until 1996, and the rock group Goblin would eventually become Argento's regular composers.
A slow-motion bullet effect is used in the film, pre-dating The Matrix (1999), as well as many Hong Kong action films.
The Italian poster for Dario Argento's earlier film The Bird with the Crystal Plumage (1970) can be seen in a street shot as Roberto drives through the city.