It is the lack of a sense of justice, the sense that the law enforcement system is corrupt and harms people rather than helps them, is what erases the trust.
If it had been a gang of muggers who had done exactly what those officers had done, Mr. Garner might still be alive because 1.) other people may have come to his aid - while no one dare intervene in his behalf against the police 2.) police may have come to his aid - rather than other officers standing around watching and 3.) he might have gone CPR.
In this instance, those officers were worse violence against him and put him more into helplessness than had he been attacked by a gang.
That does not build trust when you might have to fear the police most of all.