The individual had not established himself as a lethal threat as Brown already had by trying to take the Officers weapon.
Nor was the guy trying to advance on the Officer but trying to get away.
Regardless it is pretty much irrelevant.
What O'Donnell says is irrelevant as he did not shoot him while fleeing.
No credible witness even says he did. And forensics certainly does not support that the did.
All the shots were from the front.