In both cases the law has to decide if there was a case to answer, as per due process. In both cases the decision whether or not to indict was given over to a Grand Jury. This was as open as the decision could be, left up to the discretion not of a federal prosecutor with an agenda, but to a jury of his peers, exactly the same as he would face in court. In both cases they decided there was not grounds to indict. This means a jury decided both that they did not believe there was a case to answer, and that in a court the officer would be found innocent. That is democracy, that is law. It is not a miscarriage of justice, as the law was followed to the letter. What would be a miscarriage of justice would be if the case was reopened on the frankly ridiculous grounds that this is somehow a civil rights issue.
I am also sure that whatever evidence was provided to the juries, it was far fairer and more accurate than whatever has appeared in the media. Therefore, respecting their decision is not only respecting the law, but respecting the fact that not everything is as simple as it appears to be on YouTube.