RE: who rightfully killed this deer
I wasn't there so I'll try to not post just based on what you've said. First the letter of the law. Around here it's whoever tags it first. Notice I didn't say anything about who shot it. If you pressed the issue I'm sure a LEO would say whoever put the first lethal hit.
Second there is the spirit of the law. The first guy that shot put a bad shot on it, sure. But once he hit it, it should probably be his especially among friends. I've got hunting partners that I've hunted with for years and never have we had a dispute. We decide who's deer it is before the first shell flys and that's who's deer it is. It shouldn't ever be open season to just riddle a deer with bullets and then try to work out who got it first. Based on that I would say the deer belongs to the first guys hands down. The second guy if he was a real friend I don't think would even dispute it. However if I was the first guy I would definitely offer some meat to the first guy.