If he didn't know what the guy would do next, hold him at gun point and tell him to back off. But you don't shoot him like he did and that's why he's found guilty, be broke the law and killed someone without the requisite prongs of deadly force use present.I'm pretty sure that things happened really fast and the guy laying on his back had "NO" idea what the guy would do next, He already assaulted the guy.
Personally, The shooter should "NOT" have confronted the guy in the first place. He is "NOT" the Parking POLICE.
You don't get to shoot people for what they may do next. It's just that simple