Vincent Cassel was frustrated by the script changes during shooting, to the point of admitting on the DVD bonus features that he didn't fully grasp the plot of the film. This led to the beginning of his falling out with Mathieu Kassovitz, ending their professional relationship as well as their friendship.
The University library is named Theodor Korner, after the German merchant and politician Theodor Christian Korner (1863 - 1933). His bust is seen in the library as Jean Reno enters.
Vincent Cassel's father plays Dr. Bernard Chernez, the eye-doctor
Mathieu Kassovitz: as the hooded killer who shoots at Jean Reno at the bottom of the stairwell in the house on stilts. His voice is also heard over the CB radio talking to Vincent Cassel.