The way this situation is described is disturbing. Starting with Oakland and leaning into narratives about lack of community support for the police sounds like victim blaming:
“Communities that are especially impacted by gun violence believe that the police are ineffective or indifferent, and as a result, they’re less willing to cooperate and provide information the police need to have successful investigations,” says Cook, who has several research articles on the topic coming out.
“It is undermining whatever trust there is in the police. And it’s a vicious circle,” Cook says.
OTOH, maybe the cops weren’t worthy of any trust from the beginning and it went downhill from there. 
We’ve all learned that speaking to cops without a lawyer can lead to being wrongfully incarcerated. However, Cook claims more people need to talk to the cops to help them do their jobs. I’m sure the outcome from all those cases of cops executing people on camera and rarely getting charged or convicted of any crime really improved public opinion of what kind of job cops are doing. 
Cities that hold cops accountable, put effort into engaging members of the community, increase beat cops to increase communication, and require that cops live in the communities where they work have had better outcomes. While Prof. Cook’s conclusions are front and center, this jumped out at me from much further down the page:
Researchers say key ways cities can to try to stop the downward spiral is simply investing more in homicide investigations: improving crime labs, training, DNA testing, computer modeling systems.
Those points in the article about corrupt cops caught lying and coercing people to close cases are other key reasons for the mistrust. Finding loopholes to manipulate the figures is viewed the same way. More negative opinions come from incidents of racist behavior among the city’s cops that capture the attention of the press. The reason for the mistrust is because cops have not been acting in a way that inspires it. They’ve made it clear that they are more interested in protecting and serving themselves that anyone else*, so now we see more evidence of their incompetence on display instead of copaganda. The fact that judges and prosecutors are holding them to a higher standard is good. The public should do the same, and compensate them based on performance.
Defund the police. 
*Examples of this can be found in the BLM, Buttheads, Uprising, and Defund topics.
