If a "Good" cop becomes aware of crime committed by a "Bad" cop and doesn't report it, he becomes an accessory after the fact and is considered just as guilty as the "Bad" cop. Therefore, he becomes a "Bad" cop too, and the swamp will soon need to be drained.
I don't think you realize how bad it is in the swamp. It isn't a few isolated incidents of corrupt behavior in an otherwise healthy place. The entire culture of DC is corrupt.
There is no one to report it to. It is gratifying to learn that the DOJ IG is trying to do the right thing. The IG culture in DC has also been corrputed and they tried to corrupt this guy (Horowitz). Apparently he did not fold when mutilated.