How about the actual top law enforcement agency known as the US Marshals?

The FBI was never necessary, America did not need an independent extra-jurisdictional organization to handle organized crime. Everything we think about the FBI is a media invention to characterize them as super-hero spies stopping the evils everywhere, when all they've been doing is blackmailing people with the same unethical tactics they created to take down the mob.

Since the Mob only moved into politics, since there was more money to be had, they just ended up in control of the very organization credited with taking them down.