The Ape, the Wolf, and the Fox
A wolf one day brought a fox up to the Bench for theft. The ape, who was the judge, knew well that both were knaves; so he said, “I know you well of old, my friends; and as I wish to be just, I shall lay the same fine on both of you: on you, Sir Wolf, for you have no right to bring the charge; and on you, Sir Fox, for there can be no doubt that the charge is a true one.”
Set a thief to catch a thief.