Regardless of how many times he was hit, none of them were instantly fatal, as it is 37 seconds after the ninth shot is fired, and they are still ordering him to drop the knife. In fact, they can be heard ordering him to drop the knife as they are actually tazering him.
Obviously he was down, but not out, but it allowed them to get closer to tazer him. Whether the tazering allowed them to actually disarm him, or he had succumbed to his wounds is unknown.
First of all, any gunshot wound can be fatal or not fatal...you can't tell ahead of time. LOL
Secondly, they don't shoot to kill, they shoot to make sure you are no longer a threat. How many shots it takes is irrelevant. If they wanted to kill him, they would have continued shooting him, rather than tazer him. They don't have time to make split second medical evaluations. He's either dead/unconscious...or he's not. I doubt they were tazering a corpse and yelling at him to drop his weapon. People keep pretending that the welfare of the bad guy is the priority....when it isn't.
It was a sad day, but at least the bad guy lost and no one else was hurt.