E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
That is Pisos justice. Verbally right, but morally wrong. Seneca tells us that Piso condemned a man on circumstantial evidence for murder; but when the suspect was at the place of execution, the man supposed to have been murdered exclaimed, Hold, hold! I am the man supposed to have been killed. The centurion sent back the prisoner to Piso, and explained the case to him; whereupon Piso condemned all three to death, saying, Fiat justitia. The man condemned is to be executed because sentence of death has been passed upon him, and fiat justitia; the centurion is to be executed because he has disobeyed orders, and fiat justitia; the man supposed to have been murdered is to be executed because he has been the cause of death to two innocent men, and fiat justitia ctsi clum ruat.