What is Eum Qui Nocentem Infamat, Non Est Aequum Et Bonum Ob Earn Rem Condemnari; Delicta Nim Nocentium Nota Esse Oportet Et Expedit?

Legal Definition
If one defames a bad man it is not just and right that he should on that account be condemned, for it is proper and expedient that the crimes of bad men should be known.
-- Ballentine's Law Dictionary