Section 1623 was a response to perceived evidentiary problems in demonstrating perjury under the existing federal statute, 18 U. S. C. § 1621.5 As Congress noted, the strict commonlaw requirements for establishing falsity which had been engrafted onto the federal perjury statute often made prosecution for false statements exceptionally difficult. By relieving the Government of the burden of proving which of two or more inconsistent declarations was false, see § 1623 (c), Congress sought to afford "greater assurance that testimony obtained in grand jury and court proceedings will aid the cause of truth." S. Rep. No. 91–617, p. 59 (1969). But nothing in the language or legislative history of the statute suggests that Congress contemplated a relaxation of the Government's burden of proof with respect to all inconsistent statements given under oath. Had Congress intended such a result, it presumably would have drafted § 1623 to encompass all sworn declarations irrespective of whether they were made in pro

5 Title 18 U. S. C. § 1621 provides:

"Whoever

"(1) having taken an oath before a competent tribunal, officer, or person, in any case in which a law of the United States authorizes an oath to be administered, that he will testify, declare, depose, or certify truly, or that any written testimony, declaration, deposition, or certificate by him subscribed, is true, willfully and contrary to such oath states or subscribes any material matter which he does not believe to be true; or

"(2) in any declaration, certificate, verification, or statement under penalty of perjury as permitted under section 1746 of title 28, United States Code, willfully subscribes as true any material matter which he does not believe to be true;

"is guilty of perjury and shall, except as otherwise expressly provided by law, be fined not more than $2,000 or imprisoned not more than five years, or both. This section is applicable whether the statement or subscription is made within or without the United States."

In particular, Congress focused on the two-witness rule, under which "the uncorroborated oath of one witness is not enough to establish the falsity of the testimony of the accused." Hammer v. United States, 271 U. S. 620, 626 (1926); accord, Weiler v. United States, 323 U. S. 606, 608-610 (1945). See S. Rep. No. 91-617, pp. 57-59 (1969).

ceedings before or ancillary to a court or grand jury. Particularly since Congress was aware that statements under oath were embraced by the federal perjury statute without regard to where they were given,' the choice of less comprehensive language in § 1623 does not appear inadvertent.

That Congress intended § 1623 to sweep less broadly than the perjury statute is also apparent from the origin of the term ancillary proceeding. As initially introduced in Congress, the Organized Crime Control Act contained a version of § 1623 which encompassed only inconsistent statements made in any "trial, hearing, or proceeding before any court or grand jury." When asked to comment on the proposed statute, the Department of Justice noted that the scope of the inconsistent declarations provision was "not as inclusive" as the perjury statute. See Hearings on S. 30 et al. before the Subcommittee on Criminal Laws and Procedures of the Senate Committee on the Judiciary, 91st Cong., 1st Sess., 372 (1969) (hereinafter S. 30 Hearings). Significantly, the Justice Department did not suggest that the provision be made coextensive with the perjury statute. However, in subsequent Senate Subcommittee hearings, Assistant Attorney General Wilson indicated, without elaboration, that the Department advocated "including [under § 1623] other testimony, preliminary testimony and other statements, in the perjury field." Id., at 389.

In response to that general suggestion, Senator McClellan,

"See id., at 110–111; n. 5, supra.

In its entirety, the original version of § 1623 (a) provided: "Whoever, having taken an oath in any trial, hearing, or proceeding before any court or grand jury, in which a law of the United States authorizes the oath, knowingly falsifies fact, or makes any false, fictitious, or fraudulent statement or representation, or makes or uses any false writing or document knowing the same to contain any false, fictitious, or fraudulent statement or entry, shall be fined not more than $10,000 or imprisoned not more than five years, or both." S. 30, 91st Cong., 1st Sess., § 401 (1969).

on behalf of the Subcommittee, sent a letter to the Assistant Attorney General clarifying its purpose:

"You also read Title IV not to cover 'pre-trial depositions, affidavits and certifications.' This was not our intent in drafting the bill. We had hoped that it would be applicable, for example, to situations such as [the] kind of pre-trial depositions that the enforcement of S. 1861 would present. If we included in the statute the phrase 'proceedings before or ancillary to any court or grand jury,' do you feel that this intent would be adequately expressed?" Id., at 409.9

The Government attaches great significance to the qualification, "for example," in Senator McClellan's letter. Because pretrial depositions were mentioned as illustrative, the Government interprets the term ancillary proceeding to subsume affidavits and certifications as well. But that is not the inference the Department of Justice originally drew from the Senator's letter. Responding to the proposed modification of § 1623, Assistant Attorney General Wilson did not advert to affidavits or certifications but stated only that

"[i]nclusion of the phrase 'proceedings before or ancillary to any court or grand jury' in the false statement provision would in our opinion adequately bring within the coverage of the provision pre-trial depositions such as that contained in S. 1861." S. 30 Hearings 411.

In our view, the Justice Department's contemporaneous rather than its current interpretation offers the more plausible reading of the Subcommittee's intent. Its attention having been drawn to the issue, had the Subcommittee wished to bring all affidavits and certifications within the statutory

The provision of S. 1861 to which the Senator adverted involved use of depositions in racketeering investigations. It is currently codified as 18 U. S. C. § 1968.

prohibition, Senator McClellan presumably would have so stated.

Finally, to construe the term ancillary proceeding in § 1623 as excluding statements given in less formal contexts than depositions would comport with Congress' use of the phrase in a related provision of the Organized Crime Control Act. Title II of the Act, 18 U. S. C. § 6002, authorizes extension of immunity to any witness who claims his privilege against self-incrimination "in a proceeding . . . ancillary to" a court, grand jury, or agency of the United States, or before Congress or one of its committees. See n. 2, supra. Although neither the House nor Senate Report defines the precise scope of § 6002, they both specify pretrial depositions as the sole example of what would constitute an ancillary proceeding under that provision. H. R. Rep. No. 91-1549, p. 42 (1970); S. Rep. No. 91-617, p. 145 (1969).

Thus, both the language and history of the Act support the Court of Appeals' conclusion that petitioner's September 30 interview "lack [ed] the degree of formality" required by § 1623. 577 F. 2d, at 123.10 For the Government does not and could not seriously maintain that the interview in Canges' office constituted a deposition. See Tr. of Oral Arg.

10 In arguing that petitioner's September 30 interview was an ancillary proceeding, the Government relies on United States v. Stassi, 583 F. 2d 122 (CA3 1978), and United States v. Krogh, 366 F. Supp. 1255, 1256 (DC 1973). The defendant in Stassi was convicted under § 1623 of making statements in a Fed. Rule Crim. Proc. 11 guilty plea hearing that were irreconcilable with his declarations in an affidavit supporting a motion to vacate sentence. Without adverting to any legislative history, the Court of Appeals affirmed on the theory that a false affidavit "offends the administration of criminal justice as much as [other] false material declaration[s]." 583 F. 2d, at 127. Insofar as Stassi's analysis is inconsistent with our decision here, we decline to follow it. And Krogh affords no support for the Government's position in this case since the court there held only that a sworn deposition taken in the office of an Assistant United States Attorney General was a proceeding ancillary to a grand jury investigation.

25. Musgrave's counsel made no attempt to comply with the procedural safeguards for depositions set forth in Fed. Rule Crim. Proc. 15 and 18 U. S. C. § 3503. A court order authorizing the deposition was never obtained." Nor did petitioner receive formal notice of the proceeding or of his right to have counsel present."2 Indeed, petitioner did not even certify the transcript of the interview as accurate.18

To characterize such an interview as an ancillary proceeding would not only take liberties with the language and legislative history of § 1623, it would also contravene this Court's long-established practice of resolving questions concerning the ambit of a criminal statute in favor of lenity. Huddleston v. United States, 415 U. S. 814, 831 (1974); Rewis v. United States, 401 U. S. 808, 812 (1971); Bell v. United States, 349 U. S. 81, 83 (1955). This practice reflects not merely a convenient maxim of statutory construction. Rather, it is rooted in fundamental principles of due process which mandate that no individual be forced to speculate, at peril of indictment, whether his conduct is prohibited. Grayned v. City of Rockford, 408 U. S. 104, 108 (1972); United States v. Harriss, 347 U. S. 612, 617 (1954); Lanzetta v. New Jersey, 306 U. S. 451, 453 (1939); McBoyle v. United States, 283 U. S. 25, 27 (1931). Thus, to ensure that a legislature speaks with special clarity when marking the boundaries of criminal conduct, courts must decline to impose punishment for actions

11 Title 18 U. S. C. § 3503 (a) provides:

"Whenever due to exceptional circumstances it is in the interest of justice that the testimony of a prospective witness of a party be taken and preserved, the court at any time after the filing of an indictment or information may upon motion of such party and notice to the parties order that the testimony of such witness be taken by deposition...." The language of Fed. Rule Crim. Proc. 15 (a) is substantially the same. 12 See 18 U. S. C. §§ 3503 (b), (c); Fed. Rule Crim. Proc. 15 (b). 13 See App. 46; 18 U. S. C. § 3503 (d); Fed. Rule Crim Proc. 15 (d).