Showing just a very few of the times cops have murdered someone and probably lying about why they did and then watching as the attention on the story drops off before they drop the charges. I guess after Rodney King’s cops got off from being held accountable nothing that happens today should surprise us. I can not even imagine how it makes the families feel when that happens. And seeing so many videos of cops killing people when they didn’t have to well what are people supposed put their anger and anguish?

when the railroad was being built there were a lot of transient railroad construction workers - no families, no roots. This attracted a lot of petty crime. The police force was very corrupt. Criminals paid off the police routinely to look the other way while homes were burgled and drunks were rolled - everything was allowed just as long as no one was killed. Eventually people got sick of it. The entire police force was fired and totally honest police were hired in their place. The result was an epidemic of unsolved murders. The inexperienced but uncorruptable police forced the criminals to resort to violence while not having the knowledge base to solve the resulting murders. After a time the old police were rehired. The situation ended when the railroad was completed.
This is nothing like the present situation, but perhaps the differences should be examined. We all have heard the criticisms - police live in suburbs and drive around in cars. They know little to nothing about the communities they police. They are essentially never punished for their misbehavior. Many are combat veterans, having vastly different training and experience. Civilian police training is highly problematic - cops are trained to give testimony designed to sound impartial and professional - in essence to lie convincingly, (I was a taxi driver. As such I witnessed something like 200 traffic trials. I never heard a police officer tell the truth, except by coincidence)thus they are always believed.
Then take our pop culture. Television perpetuates a myth about our police. Every tv cop show starts with a criminal performing some heinous crime, usually with a gun. For 50 minute the community is helpless, then in the last ten minutes the hero (with a badge) shoots the bad gut and all is well with the world - until the next atrocity. I believe that this started as just lazy writing, but it quickly turned into outright propaganda.
Something terrible happened around 1960. Watching the policeshows and war movies of the 1950s one sees a refreshing realism, which is totally lost in the 60s. Take Perry Mason as an illustration: in the first season or two Berger and Tragg are the enemy - totally unethical. For Mason to win he not only had to defeat a malicious prosecution, he had to reveal the true killer; do the job the police and D.A. refused to do. But soon Berger and Tragg became Watsons, inadequate allies that benefited from Mason's brilliance. Mason was transformed from the hero into a super cop. A similar thing happened when Dragnet went from radio to television. Joe Friday morphed from a paragon of good (super competent) policing to an uncontradictable authority figure. By the 70s this was universal. As a further illustration look at the gender stereotyping - What is the gender ratio of murder victims on television? 10 - 1 female? 20? When a male is killed on television he is usually himself a criminal or a bank manager killed in a robbery or some such. In real life the ratio of male to female murder victims is 7 - 2 male. But male victims do not carry the emotional impact of female victims. (who are almost always young and attractive) This is not just lazy writing, it is intentional.