Ok, so he murdered the robber when he posed no threat to anybody. I guess vigilante justice is A-OK in the USA
If security footage corroborates with this, then the shooter has a reasonable cause to fear for the safety of his wife, and he was nothing short of brave to call to the robber and neutralize him. If footage shows this to be false, then the shooter should be arrested. I think it's pretty clear-cut.
I got two options: 1, go and shoot the motherfucker. 2, I can call my wife and tell her to hold off on coming to Waffle House. Who in their right mind would choose option 1, unless they dream of being one of those good guy with a gun and a hero? He put everybody in that Waffle House in danger when he did that. Any stray bullets from the AK-47 could have easily went into the Waffle House or elsewhere, and injure/kill innocent bystanders.
But let's think about this. What are the chances that his wife would get hurt by the shooter anyway? Even if she was 20 seconds out, the shooter would have been long gone by then. I doubt he would stand around and watch for anybody to pull into the Waffle House parking lot so he can shoot them.
This is just a guy who has always dreamt of using a gun and probably had fantasies of what he would do in a situation like this. The situation presented itself, so he went after it. He should be charged with murder.