I know a guy who was a bouncer at a bar where something similar happened. Some idiot started a fight instead of just leaving, a bouncer put him in a choke and the guy died.
The cops know it can happen and they know they are not supposed to use chokes like that, it is part of their training, remember that scene from training day where Denziel Washington makes a remark about Ethan Hawkes character using an illegal choke? Almost every cop in every somewhat modern country is told not to fucking do that to people because they can die or suffer brain damage.
Every cop there should be charged with criminal neglegence or manslaughter.
Also, if it was a white guy no one would give a shit, I hope al sharpton gets sodomized by a freight train.