I get the concept that someone resisting arrest may need to be restrained forcefully. I don't get how it's remotely acceptable for that restraint to end in the man's death. Again, it's a shocking procedural concept. The police are there to help bring people to justice, not to summarily kill people.
When it came to the Ferguson case I had some sympathy for the Grand Jury's decision, because the evidence was sketchy at best. Here it seems clear-cut that there ought to be charges at least of manslaughter to answer. And this was only about whether or not charges should be brought, too -- there would still have remained the possibility that the police officer in question would be cleared at trial.
There is something fundamentally wrong about the way all such cases seem to be treated by Grand Juries -- and, so, by US citizens -- that essentially means that the police are getting away, time and again, with what should amount to murder. Killing petty criminals is not part of the job description.