I don’t think the knee on the neck is the cause of death. If the cop was putting a lot of weight on the face down victims back, it could have killed him by positional asphyxia. Anyone routinely involved in restraining individuals (LE, Corrections, Mental Health) should be aware of that potential danger. If the prosecution can show the cop received documented training on positional asphyxia, it will be harder to defend his actions.
I have had a knee in my neck in a very similar position. Held for a few minutes I could easily see it leading to death. That is not the kind of maneuver you employ long term and the cop should have learned that in his defensive tactics class.
That said ...
1. I really don’t think the cop was intentionally trying to kill this guy despite the commentary here and among the rioters claiming he was. Looks to me like he was criminally careless, and appears to be deserving of prosecution, but I don’t think he set out to murder his victim.
2. A crowd repeatedly berating and telling the cops what to do (even if, as in this case, the crowd were completely right) and berating them is going to tend to make those cops dig in. I don’t know that the cops would have been more attentive to their victim had they not had a crowd berating them, but it definitely didn’t help. I’m not sure how an outsider could intervene in this kind of scenario without making things worse. In some neighborhoods surrounding police trying to conduct an arrest and yelling at them is kind of a sport, but sometimes it is justified.
3. Overreacting when scared is not limited to police by any stretch.
AmbulanceDriver,
How would that solution change this kind of situation? The cops are not protected by immunity in this case and all involved have been fired and at least one appears to be facing prosecution. Have to watch the case, of course, but at this stage I don’t see any indication that this is being covered up or kid gloved.
Also, civilian oversight boards are already a thing. Members tend to be good looking, sensible types, above average in every respect.