The issue isn't that "there are a few bad apples" but half of the basket is rotten to the core. Until the police and systems that regulate police are completely overhauled, we the citizens should not trust the police. The number of "bad apples" is too high to allow the citizens to have confidence in law enforcement.
If three people came up to you and told you a slightly different story but you know one of them is lying. With that risk, do you think it is safe to bother to believe any of them? Even worse is that the other two might be going along with the lie to keep their jobs or not be ostracized by their colleges.