When Brossard searches the killer's wallet, we can see 500 francs banknotes with the head of Pierre and Marie Curie. This kind of banknote was released in 1994 and the action takes place in April 1992.
While even Michael Caine would be too young to play a person of this era in history he is believable; but Charlotte Rampling's character would have to be at least 65 to have been part of this atrocity and be Brossard's wife.
When Brossard kills the assassin, he removes the assassin's passport and places it in his right pants pocket. He removes the passport from his left pants pocket while he is sitting in the car at the abbey.
As Brossard is about to place the body of the first assassin into the car, he lifts the dead man's arms into the air in order to sit the body up. As he lets go of the arms, they do not immediately drop as they would for a dead man. Instead, they hesitate, then slowly drop to the ground.