Three points:
One: The video appears to show that the perp was veering away from the cop when the first shot was fired. Maybe that's true, maybe it's not. That's for a jury to decide.
Two: The video appears to show that the cop continued to fire after the perp had fallen to the ground. It can be argued that the perp was still a danger to the cop. But again, that's for a jury to decide.
Three: The DA claims that the perp's knife was folded into the handle when he was shot. If that's true, a jury will convict in less than an hour.
I used to shoot with a Highway Patrol officer, many years ago. We went to the range a time or two. He told me he once had a guy about 50 feet away with a knife. Both this trooper and his supervisor had their weapons drawn and on the guy. The guy told me, before he knew what happened, the guy got to him and stuck him with the knife. I don’t know what happened to the knife-guy. He may have told me but I don’t recall.