It seems that the FBI, CIA, and LAPD were having a discussion on which agency was the best when it came to searching for and finding wanted individuals. They couldn't come to any agreement so it was decided that they would hold a competion. They released a rabbit into the woods. After 4 weeks the FBI returned after turning over every leaf and twig and interviewing every squirrel, deer, fox bear etc. and documenting every piece of evidence they could find, proclaimed that rabbits don't exist. The CIA then went out and turned over every leaf, twig etc, interviewed every animal for miles around, and after 2 weeks burned down the forest and proclaimed that rabbits don't exist. The LAPD then went out and returned after 2 hours dragging a bear in handcuffs. The bear looked like he had been a few rounds and had seen better days. The bear was heard to say"Ok Ok I'm a F%#@ Rabbit!
Not a slam to any other agency, I just heard this one and thought it was funny.

I heard it was the ATF instead of the FBI and they burned the forest down to apprehend the rabbit.

Otherwise, still funny as hell.

My personal favorite variation on this joke:

Department of Justice holds an national competition for Best Law Enforcement Agency.  The top 3 finalists are the CIA, the FBI and LAPD.

Final Challenge, Find and apprehend 1 rabbit in a 1 square-mile plot of Forrest.

The CIA airdrops 2 million dollars worth of remote sensing equipment.  They use numerous Animal, Vegetable and Mineral informants.  They spend 2 years developing detailed infra-red satellite imagery.  In the end, they produce a 681 page report concluding that rabbits, in fact, do not exist.

The FBI surrounds the forrest and, utilizing Negotiators on loudspeakers, commands said rabbit to exit the forrest paws-up and surrender.  They continue this for 2 months.  At the end of the second month, they burn the entire forrest to the ground and proclaim that "The rabbit had it coming."

The LAPD sends 2 SouthCentral Officers into the forrest.  A half hour later, they emerge with a badly beaten bear in hand-cuffs, screaming "Ok Ok, goddamint, I'm a fucking rabbit!"