There are several videos from different perspectives. You'll have to link me to the one you're talking about. I can't really tell from what I've seen whether the officer fired at the split second he turned and either pointed or fired the taser that him or if it was a few second later.
But my point is this: he was RUNNING. He wasn't interested in harming the police. The taser he took was a non--lethal deterrent that he was using to get away. There was no need to shoot him. They could have picked him up later. They didn't even have to chase him when he ran. He didn't have a deadly weapon and they had his address.
Lethal force can't be used to prevent an escape except in narrow situations where the person is suspected of a violent felony and is armed with a deadly weapon.
Quoting
SCOTUS here:
This was an inappropriate use of lethal force.