It could be that the one shot did not stop the man but only slowed him enough to allow the man [now] without ammo to retreat, while still in reasonable fear... I know I'd be on the retreat after expelling my ONLY round of ammo.
I'm thinking that he was initially arrested because the dead guy was at home and this guy came over to his house (to pick up his GF) and there was a feud between them already. Not saying it's right, only that it may have looked like the living guy showed up looking for trouble.