Did they ever establish that his friends were in danger? Were any of them injured?
Here is an academic question: Suppose the man who was hit by bullet fragments, happened to have a concealed carry permit, and also had his pistol with him. He hears the shot, feels the wound, and sees a man lying on the ground with a pistol pointed in his direction. He shoots the man on the ground.
Who is at fault in this scenario?
The ones hit by fragments have civil actions against him.
They would also have been justified in defending themselves as as you say they would reasonably consider themselves under threat if they didn't know what had prompted the shooting.
I rather suspect he got convicted because of the large number of people around when he fired.
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His best defense, yes. If he weren't trying to rescue friends he most certainly would have been crucified here.