I'm not so sure:
1. They were still within proximity of his property. If he goes to theirs, he is now trespassing, and it is obviously premeditated. Murder 1 would probably stick then, and it probably should.
In this case, they were still within proximity; they were possibly still on his property when he took the shot.
He has no moral (maybe legal, maybe not) obligation to wait for them to wound him or make good on their threats, he assessed what their intentions were and perceived a threat. They could have been all getting into the car to grab a few handguns out of the glove box to go and finish him off. They could have been plotting to go back in and kill him right then seeing as they already would be hit up with a felony or two and he could ID at least one or two of them. It is not his obligation to wait until they make a third attempt to inflict serious bodily harm on him. They very well may have said, "we'll be back" while he was lying there after being beaten with some brass knuckles, and then they departed. A reasonable person may assume that either they meant at a later time that night, a later date or even a few minutes. So he arms himself and goes out, sees them in the car, and whatever transpired convinced him to shoot. They may have said something, they may have said nothing, they may have given him some good tips on planting squash during the fall, we don't really know.
What we do know for a fact is that he was assaulted twice that evening by members of this group, the second time with a deadly weapon, both times in his own home. Brandishing his rifle did not serve as a deterrent as they came back, with help (though it is unclear if the newcomers into the group knew about the firearm or not at that time). His home was broken into and this group of people that assaulted him trespassed upon his property.
All the shooter did was have a party, argue with a girl over her keys or purse, brandish a rifle and went to bed.
Sorry but all we have to go on is some media accounts, a jury decision and speculation. We can speculate because we are not determining his guilt or innocence, the jury has already done so, we are simply discussing this because it is interesting and this is a discussion forum.
In this discussion, I'm going to give the shooter the benefit of the doubt that he acted as I would have and felt that they posed a reasonable threat to his life or physical well being, and I will trust the jury that he acted within the scope of the law. Thus, I rule it a good shoot.
I agree with the prosecutor as well. He thought he either had a case, or decided to charge Hill with something he knew would never stick as one could not really prove premeditation for 1st degree murder, either way, he brought his case before the jury, who then found Hill not guilty. If it was correct for the DA to charge Hill, then, as they were most likely acting on their conscience, the Jury was right to render a not guilty verdict, that's the point of a jury.
But you say they were leaving, leaving to go where, to get what and to do what? Is Hill supposed to wait for them to come back armed a few minutes later before the police can arrive after he dials 9-1-1, so he can play out someone's Rambo fantasy in his front yard and hope he makes it through the night?
Judged, not carried. YMMV.