Well, the other two stories are unlikely, but I suspect Maxime was shot at close-range. Perhaps it was not pre-arranged before that night. Perhaps, despairing, they had planned some sort of...murder-suicide? In any case, if ANYONE close-by shot Maxime by any form of his own will, it would have to be someone like Saint-Just. I doubt Maxime would trust anyone else like that. And Saint-Just DID cry (or at least get teary-eyed) over Maxime later.

Perhaps it's my romantic imagination talking. >_>