Any normal person who shot an unarmed person when they were no real danger to them, and other armed police were standing behind them would surely face murder charges.
There is simply no way that Officer Byrd can truthfully claim he was in danger. He may by lying to himself, or trying to cover up his crime, but he was not at any risk of injury from Ms. Babbitt.
He's going to insist that with a backpack, she could (not illogiocally) be a suicide bomber ready to go off. Regardless of any other stipulation, she really was where she should not have been. And that is not illogical, either. The other cops should have grabbed her and hustled her out, along with everyone else.
Hate to have to say this, my FRiends, but it is so.