The law enforcement agencies of the United States are legendary for investigating themselves - the Defense Department investigates Abu Ghraib, insists that it's just a few bad apples; the LAPD investigates racism post-Rodney King, finds things are really just swell. Interestingly, W. Mark "Deep Throat" Felt was way ahead of his time. After leaking important information to Woodward and Bernstein, Felt was tasked with investigating the source of The Washington Post's leaks. That's right. Felt was tasked with investigating... himself.
The Nation has more, but I'm slightly (slightly) comforted by the knowledge that amusing stupidity in government can still make me laugh.