The Public Defenders system is already chronically underfunded, understaffed, and far overworked. Sadly I don't think they would be the best avenue for trying to hold the police to account.
Sounds like there needs to be something like "civil forfeiture" for the Public Defenders system, allowing them to seize the assets of suspected dishonest police and police departments.
Which they can then either keep, or sell off to raise funds for themselves.
Which they can then either keep, or sell off to raise funds for themselves.