If the perp still had gun in hand, that last shot was not perfect police work, but probably ok for a layperson who will claim to have been scared shitless that the guy would jump up and start shooting. Making sure the threat was over. A police officer would have stepped on his gun hand and cuffed him even dead, but the layperson just put in another round to be sure. At least that would be my argument.
From the video, it appears that the defender noticed that the criminal had dropped his gun and that the defender had retrieved it before firing the final round.
That’s going to be hard to explain.