[pydry]

Local internal affairs departments don't work because your career is dependent upon this corrupt judge, DA, cop in your area with whom you will work again. You're incentivized not to look too closely because your career is on the line. Plenty of good cops who have uncovered corruption have been personally targeted this way.

In a national department? You get to the top by putting dirty cops in jail. Your boss's boss does not need to maintain an good relationship with a judge in Georgia. They win in their career by putting more dirty cops in jail.

The more national and centralized and separate from the rest of the police a department like this is the more ruthless it can be.