I would have to have more information in my investigation before drawing the conclusions that the mob mentality is drawing. Why was it necessary to make an arrest? Why was it necessary to take the prisoner to the ground? How hard was it to restrain the prisoner? Personally from what I have seen so far, after securing him I would have rolled him to a recovery position. If the officer didn't have articuable cause to arrest and use the force he did, then charges would result for assault, false arrest, criminal negligence causing death and possibly more. I do not see any evidence that there was an intent to cause the guy to have a heart attack though. The cop is not a very big or strong looking guy and the prisoner appears to be huge, so this cop could not have killed the guy from the restraint position he was using, as the autopsy confirmed. I am not this cops lawyer so I'm not picking sides. All I've said from the start is don't get tunnel vision. Investigate first and then draw conclusions based on all of the evidence.
I shall not be in any rush to judgment because justice is not found that way. Only professional investigators and a court of inquiry is capable of informed judgment. The "court" of public opinion is almost certainly a guarantee of injustice, and is exactly why we enjoy Constitutional law, which prescribes "innocent until proven guilty."