Acquitting the guilty convicts the judge.

[Iudex damnatur cum nocens absolvitur.]

Publilius Syrus (d. 42 BC) Assyrian slave, writer, philosopher [less correctly Publius Syrus]

Sentences [Sententiae], #296
    (Source)

Motto of the Edinburgh Review. Alt. trans.:

• "When the guilty man is let off, the judge stands condemned."
• "The judge is condemned when the criminal is acquitted." [tr. Lyman (1856), #868]

There were multiple collections made of Publilius Syrus' Sententiae in Antiquity and the Middle Ages. This appears in all of them, but often with different line/sentence numbers, incl. #256 and #257.