As of 2008, in the US,
there were about 765,000 state and local cops, and more than 120,000 federal cops. As of 2012, there were about 18,000 various state and local law enforcement agencies. There are
approximately 400 police killings each year, so far as I can find. We don't know how many are justified, so let's just assume for the sake of argument that every single police shooting every year is an unjustified murder. This means that out of 885,000 officers nationwide, 0.045% kill someone each year. Say they have an average field career of 30 years, so let's multiply that by 30. Assuming it's spread evenly and one cop only ever kills one person, so we're capturing as many cops as possible as killers, that's 1.36% of cops that kill someone during their career. Again, that's assuming that every single killing, 100%, are unjustified.
How many police agencies harbor these 1.36% killers? Each year, if they're spread evenly among agencies, 2.2% of agencies harbor these assumed-to-be-bad killers. But they're not evenly spread.
Most are concentrated in places like Chicago and Phoenix. But you're just going to condemn all the other agencies in the country for the bad things a very small portion of cops and agencies do.
If you want to condemn a bad cop in a bad shooting, after having seen all the relevant evidence, go for it; I'll join you. If you want to condemn a police agency that is protecting a bad cop, go for it. Sometimes agencies can have bad policies.
But claiming that every person who puts on a badge is somehow complicit in the very few killings (even assuming 100% of them are unjustified, which is a VERY generous assumption to your position) that happen, and that every agency is complicit in cover-ups even when most don't have any killings to cover up, is frankly immoral. You are condemning people for the actions of others that they have no control over. It's not just some benign accusation; it's deepening the divide between police and the public.
Most cops are good people trying to do good to the people. That's it. Just like you've not always called a neighboring company to complain about how they treat their employees or customers, many cops just go to work, do their job, and go home. They're not the boss. They don't control even their own agency, let alone other agencies. And here you are, condemning them all for doing more to directly help people than you or I will likely do in our lives.