The Daily Mail has excellent stills and video on the action on the street. A big guy struggles with the man with the rifle and begins to beat him down with a skateboard. He is shot in the chest and staggers off and dies. Then the "Paramedic" comes for some and gets his arm blow up. The Mail has a picture of him holding his blown up arm showing that he has a pistol in his hand! So apparently he was going to kill the shooter.
Anyway, the only decision the shooter had was whether to be present with the gun in the first place. But otherwise he was just defending himself.