Sheriff-Bullock

Judging by the third trailer Arthur is much more morally conflicted character than we were initially introduced to in the second trailer, he's very well aware that the wild west is dying with his line "This thing is pretty much over, we're more ghosts than people" and then Dutch imploring him to "keep faith" I think he'll definitely develop a conscience as the game goes on, I think he and John will probably be close friends, I think he may bring John into his way of thinking and persuade and help him and Abigail to leave the gang behind.

Doubt it, probably just some innocent bystander that Dutch killed, John didn't recall her name when the man told him, if she was in the gang he'd have known her for sure.