Ugh... dear goodness...
I have a lot of respect for the police... I would never be able to be a police officer, it is a very demanding job and they put their lives on the line quite often (though they aren't in the top 10 most dangerous jobs). IMO outside of corrupt officers all police officers are heroes, end of discussion.
But how does this stuff keep happening where the police are filmed doing something out of line, they confiscate it, and it goes missing. It shouldn't be a necessity for there to specifically be a program that immediately uploads videos to the internet as a way to reliably gather information on the police. A call to the police about a officer abusing their power should actually get a response. and Police shouldn't be able to just shut off cameras. Several states shouldn't be able to make it illegal to film the police (well ok, they try but it never passes in the Supreme court)
If they don't want to be recorded doing their jobs by citizens then why resist body cameras so strongly. If you do your job, then you do your job.
If you want to protect the privacy of a police officer who has a body camera then do what the police usually have to do and require a warrant to even look at the footage. BOOM!
Every single time I get this report of some officer abusing their power there is almost always some sort of bastardry going on. I almost wish we would just have a flat out illegal shooting by the police that didn't get this stipulations.
Real, non-joke answer
The problem comes from two directions.
From below, the police themselves close ranks when attacked, even justifiably, because of a combination of
esprit de corps and the amount of shit that gets piled on even when they do everything
perfectly, let alone all the somewhat dubious cases where the cops fully believe the officer was in the right or those cases where faulty/incomplete information made the police behavior look bad.
From above, training budgets are shot to shit (this despite the often bloated equipment budgets, due to strings on how money from a given grant can get spent) in many -if not most- major American cities, meaning that an officer that gets jailed or dismissed for misconduct is gone with no replacement, leaving the department permanently a man down. This leads to the department having a harder time keeping order, and this directly hurts the politicians that are ultimately in charge.
The pressure from below would exist in all but the most Utopian societies. Even if you have a police force made up almost entirely of saintly Officer Friendlys, the disputes between them and the ordinary citizenry would remain, and this would result in the police force being among but apart from the general population.
What
can be done is reducing the pressure from above via boosting the training budget to keep problem officers from being indispensable while reducing the workload on police by reworking the law (decriminalization or outright legalization of things like voluntary adult prostitution, less impactful drugs such as marijuana, etc.) to allow more efficient use of manpower. If a mayor doesn't have to make the calculation that not getting rid of this officer will cost X votes in the short term but getting rid of this officer risks costing Y votes in the long term then the pressure from above will ususally be "clean things up".
Other measures, such as mandatory body cameras, regular paperwork audits, and other forms of accountability are excellent tools as well, and encouraging people to take a less adversarial attitude when dealing with police (while still operating under standard self-protection guidelines such as clear, unambiguous answers, no sudden or unannounced movements, and being willing to lawyer up if things start to look iffy) will go a long way toward defusing a huge majority of potential conflicts while making it very hard for the cops to claim justification if they get out of line.