Set a thief to catch a thief

A thief knows all the tricks of the game, so it is best fitted to catch others engaged in it. A similar proverb is An old poacher makes the best keeper. Thomas Fuller wrote in his Church History of Britain: ‘Always set a thief to catch a thief; the greatest deer-stalkers make the best park-keepers.’

See also:

• An old poacher makes the best keeper