They shot him in the arm before he had a weapon.
I would say that showed intent to kill him,
and he was in his rights to self defense.
At that time, yes. But afterwards, it would not be considered so as they were fleeing the scene. At that point it is revenge, and while I'm good with that, here in Iowa it would get you multiple years in jail. I don't think it's worth it.
Groups here are working to change the laws, but not getting very far at this point.