Due to his wild reputation of being particularly difficult, the casting of Klaus Kinski on this film caused some serious apprehension to director Georges Lautner, who eventually found in him the nicest and most cooperative actor he could have dreamed of.
The song playing on parking garage attendant Kébir's office radio when Alain Delon pulls his car in is called "Bhemmou" by Algerian singer Hsissen.
Allmusic's Yuri German noted, "Film director Georges Lautner, who worked with Philippe Sarde on a dozen films, said that he was always impressed by the composer's ability to find an original musical approach to each picture. This time, Sarde, who always closely follows the editing process, suggested that they needed a strong soloist, preferably a tenor saxophone player, who would serve as a musical counterpart for the actor Alain Delon's famous good looks. Being a perfectionist, he opted for Stan Getz, one of the all-time great tenor saxophonists. Watching Getz's performance, Lautner decided to find a way to put the musician in the picture. He filmed Getz playing the opening theme, "Paris, Cinq Heures du Matin," solo, and it's the saxophonist's silhouette that appears during the credits sequence in the beginning of the film . . . The soundtrack turned out to be costly, but the director was pleased with the outcome. Sarde's instincts were right --- Getz's saxophone gave the soundtrack a lyrical, nostalgic quality --- fitting for Alain Delon's quest in the film for the sake of the past, to honor the memory of his dead friend."