The FBI was never made to combat organized crime. That may have been the excuse, but it was not the reality.
It has been corrupt since it's inception. J Edgar Hoover built it and ran it like his private feifdom. What more do you need to say about it.
Even back in the 50's it was legendary.
Anyone remember that line from the movie Clue ?
"Why is J Edgar Hoover on your phone ?"
"He's on everyone else's, why shouldn't he be on mine" LOL.
The only difference is that during the cold war they used their corruption to fight communism. When that movement rebranded itself as globalism they switched sides. But they were never not horribly corrupt.