2005. Lawyer’s Duties towards Other Parties.—The duties of the lawyer to his client do not exempt him from certain duties to other persons who have a part in the trial; for he is responsible to his own conscience and cannot act on the principle that he must win at any cost, or that the client takes all the blame for anything dishonorable that is done.
(a) Thus, respect is due to the judge and politeness to the opposite party, his lawyers and witnesses. Abusive language and improper personalities, therefore, should not be resorted to, and customary courtesies should be shown.
(b) Truth and fair dealing are due to those to whom or against whom the pleading is directed. It is contrary to truthfulness to cite statutes or decisions that are no longer in force, to misquote laws, testimony or the language of opponents, to assert as a fact what has not been proved, to introduce false witnesses or documents, to coach clients or witnesses in untrue stories, to resort to quibbles or sophistry, etc.; it is unfair to attempt to gain special favor from a judge or a jury, to make improper statements or remarks with a view to influencing the jury or the bystanders or the public; to conceal the arguments upon which one relies until the opposition has no opportunity to reply; in a word, to practise any of the tricks of pettifoggery.
2006. Concealment of Truth in Presenting a Case.—Is concealment of the truth in the presentation or defense of a case sinful?
(a) If concealment is not unjust or mendacious, it is lawful. Indeed, a lawyer should conceal such facts as would be harmful to his own case (e.g., incidents that are really of no moment, but that would create prejudice against his client), or as he has learned in confidence. This is not unjust, since the opposite party has no right to the knowledge, and it is not deception, since it does not cause but merely permits others to draw erroneous conclusions. Neither is an advocate bound in justice to point out to the opposition matters favorable to their case, of which they are ignorant or which they do not notice.
(b) If concealment is unjust or mendacious, it is unlawful. Thus, if a lawyer discovers that serious fraud has been practised or that the court or the opposition has been harmfully imposed upon, he is unjust if he takes advantage of this through silence. Similarly, a prosecutor is unjust if he suppresses facts or testimony or papers that would establish the innocence of an accused person.
2007. The Sinfulness of Introducing False or Corrupted Documents.—(a) Truthfulness is sinned against by this practice, whether the document be entirely fictitious or a copy substituted for an original that has been lost, or an authentic instrument has been changed or interpolated (see 1980 a, 1991).
(b) This practice is also against legal justice, since the law requires that no misrepresentations be made about the evidence produced. Indeed, this is a very serious matter, for, if it were ever permissible to tamper with documentary evidence, a way would be opened to frauds innumerable to the great detriment of the public.
(c) Commutative justice is offended by this form of dishonesty, if the cause defended is not certainly just; for the opposite party, since justice is perhaps on his side, has the right that he be not defeated by untruthful means. But if the cause defended is certainly just, there is not _per se_ any violation of commutative justice, since the adverse party is not deprived of anything that is his, but is rather prevented from doing injustice; _per accidens_, though, there might be commutative injustice (e.g., if the use of a forged exhibit was known to be risky and did actually lose the case for a client).
(d) Charity to self is violated by this deception, since a lawyer should not value his client’s interests above his own conscience, reputation and prospects.