At a minimum, these are needed:
State level registries of officer violence/complaints
Citizen recertification boards 1/
Residency requirements for at least the majority of the force
Body cameras worn by all and on at all times during interface with the public, video and audio
Review of current officer's records
2/
What about body cameras? Yeah, not having privacy sucks. But lots of people give up privacy for a job. 3/
I'm not saying body camera footage is all available to the public, but this should really be a no-brainer. 4/