I mean they're trained to shoot first because they're told EVERYONE is out to kill them so people committing misdemeanors are just as at risk as armed killers of being shot, and then there's instances like the thing where the postal worker was taken hostage and they just made swiss cheese out of the whole thing killing the hostage and shooting a few people in nearby cars for good measure. Even if you account for proportional differences with population, the proportion of people shot by police is still massive. Especially since in some countries the amount of people shot by police are in the single digits. Not to mention if you try to arrest a corrupt cop, chances are he works in an area that encourages that corruption and thus your life will be a living hell if you pursue things further. Or even if he isn't in a corrupt area, often people fired from one precinct are easily hired in another one. Honestly there's a LOT that needs to be improved about the US justice system, and the enforcement is just one part of the absolute mess that its in.

It doesn't help that we give them military hardware, but actual military personnel are supposed to have rules of engagement to determine if they're allowed to shoot or not. In the US, we not only don't have them train for a year like most countries do with their police, we also train them to shoot first and assume hostile intent. We've had courts declare that police are not obligated to protect you, just to enforce laws… It makes the US look like a military state. And it's not… exactly.
It's open ended enough so you CAN do that if you want to, and because the US is huge the law of averages dictate you'd find a few areas where the police are little more than legal gangs. I mentioned being in a bad area or a good area, but if you TRY to report a cop in a bad area you're going to get run out of town because you broke trust in the 'brotherhood'. Thus bad areas end up worse, especially when the bad cops get reported in good areas and go find employment elsewhere that doesn't care about what horrible things you might have done. And hell, in order to review cases of police wrongdoing, the precinct investigates itself. So it's just a huge loop of bad places getting worse and multiple news stories reporting this… and granted they SHOULD report this as it's horrific and deadly. It's… complicated.