How much, if at all, can a criminal defense lawyer cooperate in his or her client's decision to commit perjury? Courts, commentators, and bar committees have grappled with this question for years without offering clear or consistent guidelines. Any principled response must take into account some very hard questions. Under what circumstances, for instance, does the lawyer ever really "know" that his client's proposed testimony is false? Is it sufficient if the lawyer simply disbelieves his client's story, or that of his client's witnesses? Does it make any difference if the attorney learns of a plan to perjure during the trial, as opposed to prior to the trial? What actions can the lawyer properly take when he believes that his client intends to commit perjury? Is the prevention of perjury more important than loyal and aggressive representation? Can the lawyer simply remain silent, and passively allow the perjury to occur? Can he threaten to impeach his client's testimony? Withdraw from the case? Report his client's actions to the judge?
Last Term, in Nix v. Whiteside, the Supreme Court for the first time addressed several of these questions. The Court unanimously agreed, under the facts of the case, that the lawyer's refusal to assist his client's plan to commit perjury did not deprive the defendant of his sixth amendment right to effective assistance of counsel, nor of his right to testify in his own defense. A majority of the Court essayed the ethical questions as well and, in obiter dicta, concluded that "under no circumstances may a lawyer either advocate or passively tolerate a client's giving false testimony." The majority went further, however, and formulated specific rules of permissible and impermissible attorney behavior.
Bennett L. Gershman, Attorney Loyalty and Client Perjury - A Postscript to Nix v. Whiteside, 14 Am. J. Crim. L. 97 (1986), http://digitalcommons.pace.edu/lawfaculty/169/.