It is commonly said among criminal lawyers of all stripes that “there can be no immunity for perjury” or “you can’t take the Fifth for perjury.”
What does it mean?
Clearly, a witness can’t use immunity as cover for lying on the stand. So false testimony given under a grant of immunity is and should be admissible in a perjury prosecution.
But what if the witness had perjured herself last year? Can the State compel her to admit it this year and then use the compelled testimony against her?
In other words, is truthful testimony given under immunity admissible in a prosecution for an earlier perjury?
While that’s a common understanding of the state of the law among prosecutors, judges, and criminal-defense lawyers, I see no authority for, nor sense in, that position.
As far as policy is concerned, there are no better reasons to permit immunized testimony to be used to prosecute the witness for a past perjury than a past murder. In fact, there’s a good reason for truthful immunized testimony not to be used to prosecute the witness for a past murder: the immunized witness who fears that telling the truth will subject him to prosecution for a past perjury has a strong reason to continue perjuring himself, and as much as the system has an interest in past perjury being prosecuted, it has a greater interest in past perjury not being perpetuated.
As far as the law, there’s a gem of a Fifth Circuit case, In re Grand Jury Proceedings, 644 F.2d 348 (5th Cir. 1981) with this explanation:
[I]t is well established that the exception under the immunity statute, 18 U.S.C. § 6002, which authorizes prosecution for perjury, as construed by this Court and elsewhere forecloses the government from prosecuting an immunized witness for perjury based upon prior false statements. United States v. Leyva, 513 F.2d 774, 776 (5th Cir. 1975); In re: Grand Jury Proceedings, Taylor v. United States, 509 F.2d 1349, 1351 (5th Cir. 1975). These holdings, and the holdings in other circuits as well show that he not only could not be prosecuted for perjury on the ground the prior statements were false but also by clear implication the prior statements could not be used as prior inconsistent statements to prove perjury in the testimony before the grand jury.
In Texas, the state can generally prove a perjury case by simply showing two contradictory material statements under oath, without proving which one is false: if there are two inconsistent material statements, one of them must have been false. According to the Fifth Circuit, under the federal use-immunity statute, which is coextensive with the Fifth Amendment, if immunity bars the government from using an immunized statement to prove that a prior statement was false, it also bars the government from using a prior inconsistent statement to prove that the immunized statement was false. The Seventh, Eighth, and Ninth Circuits at least agree; I didn’t find any cases suggesting that immunized truthful testimony could be used as an inconsistent statement to prove prior perjury.
So the witness who perjured himself in the past is safe if, under a grant of immunity, he reveals his past perjury. Further, while perjury committed under immunity is prosecutable (and the immunized perjurious statements are admissible as the corpus delicti of the perjury prosecution), in order to prosecute the government has to prove that the immunized statements, rather than any contradicting non-immunized statements, are false.