This goes back to the argument with Davis and Dunn. If Davis makes a threat to cause bodily harm or death against Dunn, that in itself does not give Dunn legal authority to use lethal force in self defense. If Davis presents a weapon, like a firearm, which is capable of immediately carrying out that threat or attempts to leave the vehicle to make the carrying out of that threat to Dunn imminent, then Dunn has legal authority to use lethal force in self defense.
That is how the laws are written. In this scenario, Dunn is going to have to prove that Davis was making threats. There is evidence o'plenty of that. The sticky part is what follows. He has to prove that Davis or his friends were presenting an imminent opportunity to make their threat credible.
That is for the first part of the shooting. The part where Dunn got out of his car and continued to fire once the threat was stopped and speeding away. That is going to nail him period. In self defense if you use a gun for defense you shoot to STOP the threat. Not make sure the threat is dead. There is a difference. There is no problem with shooting the firearm multiple times. But to stop firing, reposition, and to fire again on a fleeing vehicle... Yah he's going to be in jail for that part. Deservedly so too.
However, that is just reckless discharge of a firearm and not murder for that. Still a stiff penalty, but not as stiff. The point of contention for topic of Dunn and Davis is if Dunn was legally justified to use lethal force in the first place. We have evidence of Davis threatening him. We don't have evidence, at this point for the public, if that was a credible threat or not.