The actor playing the doctor got cold feet during his explanation of the X-rays of Z's cranium. A real doctor, acting as an extra, volunteered to fill in and finished the scene - his only acting performance on film.
The actors falling off the truck had to do their own stunts as the low budget would not allow for a stuntman.
Due to the film's depicting a thinly fictionalized version of the murder of a Greek politician and to director Costa-Gavras being of Greek origin, the film has a lot of details that hint at the story's origin, although the Mediterranean country in which the film is set is never named. Greek songs are constantly played in the background. Greek actress Irene Papas portrays the widow even though she barely spoke any French, which is why she had very little dialogue in the film. Newspapers held by actors and other props such as beer bottles are local Greek products. There is also, in one shot, a photograph of the Greek royal family, although a light shines on it and the faces are thus obscured.
The first film to be nominated by the Academy for Best Film and Best Foreign Language Film.
Many minor roles were played by members of the crew for budgetary and logistical reasons.