Other mistake: Interior Minister Roger Frey advises Commissioner Lebel that all members of the police, military and other security forces attending the ceremonies on the day the Jackal is expected to strike will be issued with lapel badges at the last moment, in case he is going to try to masquerade as one of them. We see hundreds of such people in the next part of the film, including Lebel himself and the CRS private who allows the heavily disguised Jackal through the barricades around the site of the ceremony DeGaulle is due to attend. Only the CRS private wears a lapel badge. Not one of the other police or military officers in attendance is wearing a lapel badge of any kind. (01:58:15)
Other mistake: The Jackal goes out into a field to test his gun and adjust the sights. But the gun is then dismantled again, so the adjustments are irrelevant.
Answer: He would have just slipped away into the crowd, probably with some minor alteration to his appearance. He was a master of disguise and no one knew his real identity or what he looked like.
raywest