True, and true. The main issue in this case, though, is whether or not the teen pointed a gun at the cop. I don't think this point has been clearly established yet, given some strange circumstances I detailed earlier. If the the teen did point a gun at the officer, case closed. If he didn't, then all hell breaks loose, as we'd be facing a major cover-up happening in the middle of an already explosive situation.
One thing that would help, I think, is that police leaders re-train officers to have body cameras and dashboard cameras on at all times, and that this footage be immediately and transparently available in any doubtful case. Trust and accountability must be restored from all sides, otherwise we are all as a society headed into a lot of trouble (which has started already, like the crazy guy who shot and killed two officers in New York City).
Me, while I wouldn't endorse for a second any case of unjustified police brutality, I'd also want my home and family and city to be protected by police.
The police serve society in a very essential job (and a difficult, honorable, and dangerous and even heroic one); on the other hand, we do need our police officers to be highly trained, responsible (as in, using the right level of force required by the circumstances), and accountable if they stray (with non-malicious human error being taken into account as attenuating circumstance, but malicious and deliberate misuse of force or cover-ups being severely punished). We need our citizens to be equally law-abiding, respectful of officers when the police are doing their job appropriately, and accountable for things like violent protests and looting. We need our criminals to be caught, prosecuted, and killed when justified (as in self-defense when they are trying to kill an officer). In summary, we need a state of law where all parties behave within it.
Unfortunately as a society we seem to be currently far from the ideal I've just stated.