The police have by default a duty and responsibility to act on any situation they encounter, no matter how stressful and controversial, in a professional and ethical way that inserts justice into those situations. That said, when an officer is clearly unethical in their actions, it is up to any citizen to either fight or submit, and must bear the consequences of their decision.
As someone who knows many in law enforcement, I can say that the system is fair and just in the majority if cases, at least in the USA, and if you do your best to not give any reason to grant suspicion of foul play then you have more than a fair opportunity to win your case in court. I myself have been to court on 2 occasions and won both because I held my cool and presented my case in a respectful and factual way. Those that fought against the authority were less fortunate.
As a part of the general human population, we are all obligated to be whistleblowers. If someone is unjustly punished, we are all guilty if they are truly innocent. My thoughts on this particular matter are that the officer in question is clearly out of bounds, but the suspect may have made things better by not provoking as well. This officer has many instances of complaint against him, and I feel that the station employing him should have gotten rid of him sooner. This is all an example of when less than capable police respond to situations where utmost calm, clarity, coolness, and humility MUST be exercised by those that respond. This guy is probably fine to conduct traffic stops, but to respond to something like this was outside of his ability to remain professional, obviously.
Again, my recommendation to all that read this, cooperate with police, use your manners, be respectful, dont fight in the heat of the moment, and reserve your case for court day. You will be more than likely exonerated if truly innocent. My condolences go out to all those affected by this terrible situation, and also to those who live in places with routinely corrupt police.