Basic facts: Four white plainsclothes cops beat up a 12-year-old black girl in her own yard because they thought she was a hooker. Girl is being tried for assaulting a police officer.
It's this kind of thing that results in a large swath of American society (namely blacks, Hispanics and any whites who know any) having no faith in the police.
No matter how outrageous the police conduct is, the system protects them and their abuse of power. Gun down a black guy with dozens of bullets? No problem. Beat up a child. No problem.