Did all of the attending cops not know that cutting off a person's breathing capability such a choke hold or knee against the neck could cause an individual to blackout and possibly die ? - the cops were following local PD procedure at the time.
I certainly can see criminal negligence manslaughter in this incident - yes, me too.
He wasn't strung out high when the arrest took place, that can be confirmed by the video - you can't confirm whether or not someone has drugs in their system by watching a video. A qualified medical person needs to do a blood test.
Someone who is high on fentanyl doesn't act like that - one adverse effect of fentanyl is respiratory depression. In the worst case scenario, if someone ODs on fentanyl they can suffer chemical asphyxia.