Agree for the most part, I was assuming they have a lawful reason for contact when they had him on the ground as well when they attempted to tase him.And it might not matter at all. There is way too much missing information to even begin to determine if it's relevant or not. Was he detained? Under arrest? Was the detention lawful? The mere possession of a knife with no intent to inflict harm or injury does not warrant lethal force.
The cop who fired the shots better have some very damning information available to him that we can't see or here in the video for him to avoid criminal prosecution.
If it’s an arrest that went South and then the suspect pulls a knife and attempts to get into vehicle, I think they are ok.