(b) If the accused is guilty, he must reply truthfully, if the judge has the right to ask the question; for if the judge has the right to question, the accused has the obligation to answer, even though unpleasant things will befall him in consequence.
(c) If the accused is guilty, but the judge has no right to ask about his guilt (that is, if the judge does not question juridically or according to law, or if he questions from a false presumption of guilt), or if the accusation cannot be proved juridically, the accused is not obliged to answer. He may keep silence or evade the truth, but it is not lawful to lie.
1979. Legal Right of a Judge to Question a Prisoner about His Guilt.—(a) According to older legislation a judge had this right, and could enforce it by torture, when the common good was involved and the guilt of the prisoner was likely on account of infamy or manifest indications of crime or half-proof of guilt. In itself, this practice was not opposed to natural law and had some good results; but it was open also to many abuses. Some moralists teach that a judge cannot impose a grave obligation of confessing guilt in capital or similar cases, if the accused has otherwise a hope of escape and no great evil is likely to befall the common interests by reason of an acquittal. They argue that human law cannot oblige so rigorously as a rule.
(b) According to modern civil legislation the right of exacting a confession is denied to a judge. Thus, according to American law no person may be compelled “in any criminal case to be a witness against himself” (Constitution, Article V). In American law the plea of not guilty is not a lie, even though the accused knows that he is guilty, for, as everyone understands, the plea means either that one is innocent or that one is using the privilege of not confessing. Neither is it considered a lie to say that an unprovable charge is a calumny, for an accusation that cannot be proved juridically is juridically a calumny.
(c) The general law of the Church rules for ecclesiastical processes that, when the judge questions the parties-litigant, they are obliged to answer and to confess the truth, unless the question is not legitimate (e.g., questions about irrelevant or privileged matters, or questions made in a captious or leading manner), or the answer would incriminate the parties themselves (Canon 1743). Neither is an ecclesiastical judge permitted to put an accused in a criminal case under oath to tell the truth (Canon 1744). An instruction of the Holy Office of 1866 required that the guilty party in a case of solicitation should confess, but the instruction was directive rather than preceptive. Particular law (e.g., the statutes of a Religious Institute) might perhaps prescribe confession by an accused, but most Constitutions of Religious Institutes bind only under penalty, and, as for the rest, an ecclesiastical superior could at most advise, but could not impose, confession by an accused.
1980. Rights and Duties of Accused in Conducting His Own Defense.—(a) In Reference to Judge or Attorneys.—The accused, if questioned, may not conceal the truth by lies, ambiguities, or half-truths, since these are evil means, nor may he use evasion if he is lawfully interrogated. But if the question put to him is unlawful, he may evade an answer. It is commonly held that lies told in giving testimony or evidence are not necessarily mortal sins, as there may be no perjury committed or grave harm done another by reason of them (e.g., when an innocent man “doctors” a paper and thereby without harming anyone escapes from an unjust sentence).
(b) In Reference to the Opponent or His Witnesses.—The accused has the right to disclose secret but real crimes of the accusers, when this is an exercise of his legal right of taking exception to the witnesses as incompetent, or of his natural right of clearing himself of the charge against him. It makes no difference whether the evidence of the accusers is true or false, whether given according to the order of law or not. But he must not go beyond the limits of moderate self-defense (see 1826). Innocent XI condemned the proposition that it is probable that calumny may be used without mortal sin as a defense of one’s justice or honor (Denzinger, n. 1194).
1981. If the accused objects secret crimes of the opposition, he must beware of injustice or uncharitableness. (a) Thus, it is unjust to disclose crimes that cannot be proved, or that are irrelevant (e.g., it may be irrelevant to prove that the person who testifies that the accused committed murder is himself a fornicator, but it would be relevant to show that this witness is a liar, or dishonest, or an enemy of the accused), or that need not be revealed (e.g., if the witness’s testimony can be overcome by showing that the witness is weak-minded or under obligations to the opposition, it is not necessary to defame him).
(b) It is uncharitable to disclose a crime, if the witness will suffer far more from this defamation than the accused would suffer from the testimony. If, however, the witnesses are giving false evidence of their own accord, they take the risk of revelations by the defense.
1982. Rights and Duties of an Accused Who Has Been Found Guilty.—(a) Appeals.—It is lawful to appeal from a sentence that is unjust (whether because of the innocence of the accused, or of the illegality of the process), because appeal is a means of self-defense granted to the innocent. It is not lawful to appeal from a sentence that is certainly just, merely in order to cause delay or to defeat an adversary; but one may make an appeal when there are just reasons (e.g., in criminal cases the hope of getting an easier sentence or of prolonging life, in civil cases the discovery of new proofs, or of probable arguments against the sentence given). But one who has pledged his word not to appeal from the decision of an arbitrator should abide by his promise, and there is no appeal from the final decision of the highest court, which in the Church is the Roman Pontiff (Canon 1880), and in the State the Supreme Court.