the shooter had time to escape the threat
That is not how it works.
Time to escape is something that applies when you go back to scene e.g. you're in a fight with someone, you run away, and then you return with a gun. You cannot claim self-defence in that situation as you're effectively returning to the situation.
If someone threatens to shoot you, you're not under a legal obligation to run away. If they return with a gun, they're presenting a threat of harm which you have a legal right to defend yourself against.
Unless there is more to the story, the charges will get dropped or he will be found not guilty.