Probably because the guy was coming at him and being 6'4" he thought that a few well aimed punches and he - the officer - was gonna be out cold with the other guy in possession of his gun.
In which case he was gonna be out cold permanently.
A police officer friend told me once about an Arizona DPS officer who emptied his clip into an escapee with the last bullet going through his hand which was on the guy's chest trying to stop him, even though he had already taken 5 bullets. The last one did the job at the expense of the highway patrolman's hand.
But at least he wasn't dead.
And that guy was unarmed as well. But he kept coming, and was a similar size.
The more I hear of this case the less I think the cop has anything to worry about in a real court.
But since the "president" we elected is a thug, the likely court will be run by a Kangaroo.
I had read earlier that the initial autopsy claimed all shots were from the front...