This frequently arises in a tax crimes setting where the witness -- who may be a putative target or subject of the investigation depending upon how the prosecutor feels for that day (I'll not get into that now) -- might prefer not to be under oath and thus might want his lawyer to "negotiate" (with an appropriate Queen for a Day letter) a proffer session rather than testifying under oath in the grand jury (assuming he might even be tempted for not assert his Fifth Amendment privilege in the grand jury room). One reason is that the witness may feel less exposure under a false statement criminal regime rather than a perjury criminal regime. So, I thought I would do a quick survey of some of the issues that have concerned me about the differences between perjury and false statements.
First, the statutes:
Perjury, 18 USC § 1621(1), here.
§ 1621 - Perjury generallyPerjury before the Grand Jury, § 1623, here.
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 under this title 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.
§ 1623 - False declarations before grand jury or court
(a) Whoever under oath (or in any declaration, certificate, verification, or statement under penalty of perjury as permitted under section 1746 of title 28, United States Code) in any proceeding before or ancillary to any court or grand jury of the United States knowingly makes any false material declaration or makes or uses any other information, including any book, paper, document, record, recording, or other material, knowing the same to contain any false material declaration, shall be fined under this title or imprisoned not more than five years, or both.[I omit the balance of § 1623 which does have some interesting features such as where two inconsistent statements are made under oath, the crime does not require that the Government prove which is false except that it is a defense if the witness believed each statement to be true at the time he made the statement; the witness' ability to purge the crime by acting within the court or grand jury setting, and eliminating the two witness rule to prove perjury.]
False Statement, § 1001, here.
§ 1001 - Statements or entries generally
(a) Except as otherwise provided in this section, whoever, in any matter within the jurisdiction of the executive, legislative, or judicial branch of the Government of the United States, knowingly and willfully—
(1) falsifies, conceals, or covers up by any trick, scheme, or device a material fact;
(2) makes any materially false, fictitious, or fraudulent statement or representation; or
(3) makes or uses any false writing or document knowing the same to contain any materially false, fictitious, or fraudulent statement or entry;
shall be fined under this title, imprisoned not more than 5 years or, if the offense involves international or domestic terrorism (as defined in section 2331), imprisoned not more than 8 years, or both. If the matter relates to an offense under chapter 109A, 109B, 110, or 117, or section 1591, then the term of imprisonment imposed under this section shall be not more than 8 years.