You state that your "friend" waited 30 minutes to check-in, meaning there must have been a fair amount of people. So, you say that the situation started low and rose to the point of a possible homicide. I doubt that the other passengers would just stand there when the verbal assulting got as high as the agent jumping over the counter, yet alone the passengers stand there and allow physical assult happen.
If this is true, both the agent, airport, and airline can be fined heavily. I'm surprised that your friend is so calm about a gate agent jumping over a counter and assulting him, and HE doesn't even call the police. Yet alone have the police tell him to get lost.
If this story is true, though, contact Air France immediately as this is assult of a passenger, neither Air France, nor the law will allow it.
Have a good day. Keep us updated!
canada :-: FLYER