I don't condone or endorse the violence, however cops do this all the time. Hard to say what sparked this, possibilly a lifetime of abuse from the police and he just couldn't take it anymore and snapped. Maybe he built up a life worked hard only to have everything taken away, maybe they killed someone he cared about, It must have been something pretty big for one to take on a losing battle such as this. Police have endless backup and all the money and resorces that they basically stole from those like me and possibally you.
Police: The Domestic Monopoly on Violence- https://www.youtube.com/watch?v=t8DTPdeFkbw
Many people join the police because they are enamored by images of protecting the innocent, punishing the guilty, maintaining order, promoting peace, serving and protecting the people etc. It is also fun to believe in the Tooth Fairy, Santa Claus, and the Easter Bunny but it is not encouraged to base our future professions on such myths and eventually we must shed them. To believe, in our adult life, that the primary function of police is to perform the aforementioned is to be plagued with a severe form of schizophrenia and a selective understanding of reality. In economics we understand that people act according to incentives and that by thoroughly understanding those incentives the result of those actions can be more or less predictable. If I give a man money to not work, is he likely to continue seeking employment or to abandon such efforts? If pharmaceutical representatives shower a physician with luxurious gifts the more he prescribes a certain medication is likely to prescribe more or less of that medication? If fascistic special interests banks are given cheap currency in the form of Quantitative Easing and then told by the Federal Reserve that they will be given a greater interest rate if they park it in their reserves, are the banks likely to lend that currency out or park it in their reserves? If fascistic special interests banks are told that they can gamble with the people’s currency in the massive derivatives casino, lose trillions, and those funds will still be secured throughout colossal criminal bailouts at taxpayer’s expense are they likely to gamble recklessly in the derivatives casino or be more cautious with the people’s hard earned currency? I hope the trend is clear.
The people do not voluntarily fund the police; rather they are coercively funded through the theft of taxation. Their salaries will always be guaranteed regardless of abuse or cruelty towards the people. Therefore the incentive is not about pleasing the customer in any respect but about pleasing their superiors and political masters. When this is understood then the rise of the police state, the militarization of the police, and the flooding of police brutality videos is not surprising. It is but a natural result of incentivized human action. “Government” is the giant exception to the law of morality and the enormous incentive to waste, inefficiency, and barbarity to which we all must contend. Eliminate the paradigm of systematic predation and all the wretched hydra heads will inevitably die. Stop funding wickedness with your participation and support! What is done violently through aggression is always inferior to that which is done peacefully through voluntary interaction. Good ideas do not require force.
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Fun Factor : Now you have a choice in chat, factor that
Shake it off, shake it off 
