This is obviously idealistic and impossible in the real world (given the size of a police force). What is needed is a system that gets rid of bad apples with time, instead of letting them thrive and corrupting other apples.
The problem with getting rid of bad apples with time is the amount of damage even one bad police officer can do given half a chance, and even if they are punished for what they did it would not erase the bad things they have done. Policing violations are often violent and the effects long lasting.
This is an industry where you can murder someone, get paid leave for it, eventually let go without losing retirement benefits, and then get hired the next county over.
This is obviously idealistic and impossible in the real world (given the size of a police force). What is needed is a system that gets rid of bad apples with time, instead of letting them thrive and corrupting other apples.