In Rome, prosecutorial misconduct was a serious offense. Under the Remmian Law, a prosecutor who failed to prove his case would have his forehead branded with the letter, "K," for calumniator. Cicero, Murder Trials (Michael Grant). The laws of Rome read:
Tit. 16. Concerning the Turpillian Decree of the Senate and the dismissal of charges.
The recklessness of accusers is detected in three ways, and is punished by three penalties; for they either calumniate, prevaricate, or withdraw.
(1) To calumniate is to bring false accusations. To prevaricate is to conceal true crimes. To withdraw is to entirely abandon a charge.
(2) Punishment is inflicted upon calumniators by the Remmian Law.
(3) He who does not prove what he alleges is not immediately considered to be a calumniator, for the investigation of the offence is left to the judge, having jurisdiction of the case; who, if the defendant is acquitted, begins to inquire into the intention of the accuser, and why he was induced to bring the accusation; and if he finds this was due to a just mistake, he must discharge him. If, however, he should ascertain that he evidently has been guilty of calumny, he must inflict upon him the penalty of the law.
(4) The decision of either of these points is disclosed by the words of the judgment. For if it is as follows, "You have not proved your allegations," he spares the defendant; but ff he says, "You are guilty of calumny," he condemns him; and even though he may add nothing with reference to the penalty, still the power of the law will be enforced against him. For (as Papinianus held), the question of fact depends upon the discretion of the court, but the infliction of the punishment is not left to his will, but is reserved for the authority of the law.
THE ENACTMENTS OF JUSTINIAN. THE DIGEST OR PANDECTS. Book XLVIII. (S. P. Scott, The Civil Law, XI, Cincinnati, 1932 ).