The police shouldn't be associated with the Nazis here. There's no wide scale organised plan to wipe out an entire race. The number of truly rotten officers is in the minority or there would be more bright line evidence of horribles. Most actions caught by police aren't outright actions of intentional corruption or malice, they are improper or bad policing that goes unpunished, which is the real problem.
You can't be expected to punish the police when you need them to do your job, which is the position DAs are in. If they were to lose the trust if the police then they wouldn't have the super they need to go their job. A statewide role of internal enforcement that's separate from the DA and is an unelected role appointed by the governor or legislative body would likely be the best one could do for this role and provide the freedom to do the job effectively.
Add to that punishments should come out of the insurance funds for the force meaning police organizations that are truly terrible would get shut down when they could not afford their insurance. Also a national police database with all punitive actions against officers that is permanent and not removable unless ordered by a judge would go a long way to prevent officers who get punished in multiple locations from just moving to a new job.
