If a law enforcement officer stops someone on the street and asks questions related to an investigation, the person is not under oath. The person therefore presumably cannot be prosecuted for perjury.

Assuming the person decides to respond to the questions, is there any federal law requiring the responses to be truthful? If so:

  • What law or laws apply?
  • Does the law supply a definition of "truth"? Must it be "the whole truth and nothing but the truth," or is there a different standard?

One reason for this question is interest in the degree of inequality between an interrogating officer and the subject of the interrogation, in light of the fact that the officer is allowed to lie.

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    "One reason for this question is interest in the degree of inequality between an interrogating officer and the subject of the interrogation, in light of the fact that the officer is allowed to lie." - The subject has the right to remain silent, and would be well-advised to exercise that right immediately.
    – Kevin
    Commented Mar 19, 2016 at 5:43
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    Just give them wrong directions to the nearest donut shop. That will fix them up.
    – David
    Commented Mar 19, 2016 at 12:31
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    @Kevin of course. But dishonest police might and often do lead suspects to believe that their best hope is to tell a story. Sometimes, the story is a fabrication. If someone incriminates themselves under those circumstances, I don't blame the suspect for failing to assert 5th amendment rights. I blame the interrogator.
    – phoog
    Commented Mar 19, 2016 at 16:03

3 Answers 3


This is one of the things Martha Stewart was convicted of. 18 USC 1001 is the US federal law requiring truthfulness. That statute forbids you to falsify, conceal, or cover up a material fact. One limitation on how broad this law is, is that it has to be a matter "within the jurisdiction of the executive, legislative, or judicial branch of the Government of the United States". If your neighbor is an FBI agent and he asks if you're the one who broke his window, and you lie, that's not a federal matter. Another limitation is that the lying has to be material.

The essential part of the law is subsection (a). Subsection (b) then states an exception:

(b) Subsection (a) does not apply to a party to a judicial proceeding, or that party’s counsel, for statements, representations, writings or documents submitted by such party or counsel to a judge or magistrate in that proceeding.

Then you also owe a lesser duty of truthfulness to the legislature.

Taking note of US. v. Yermian, it is not required that the person you lie to be a federal officer. Yermian lied to his employer, who was a defense contractor, and the fact that the relevant form was submitted to the government for scrutiny is what made it a matter in federal jurisdiction. Comparing the wording of 1001 to the perjury statute, the operative expression for perjury involves statements "which he does not believe to be true", we can see that the perjury statute requires telling the literal truth (see Bronston v. US), which allows so-called lies of omission (of a particular subtype: much more could be said about that). In contrast the lying statute forbids both literally false statements and concealing of the truth.

I don't have cases at my fingertips that indicate how broad your truthful answers have to be, for example if you think the FBI is trying to put away a friend and ask you about what he did on June 14, and you know that he did a bad thing on June 13, would it be lying in the relevant sense to conceal that fact which they didn't ask about.


A session of perusing cases has led to a tiny bit of further information. A literal reading of the statute says that you are in violation of the law if you falsify a fact (sloppy epistemology, unless it refers just to altering records and evidence), or conceal a fact, and the courts recognise this as a fundamental division. As for falsifying, the way that has been applied is to refer to cases where the accused makes a statement which asserts something that he knows to be untrue. Thus, saying "No" to a question when the truth is "Yes" is a violation.

A propos concealment, in US v. Diogo 320 F.2d 898 the court states that

False representations, like common law perjury, require proof of actual falsity; concealment requires proof of wilful nondisclosure by means of a 'trick, scheme or device.'

This case is pre-Bronston so there is mixing of concepts from perjury law and lying law, which would not happen now, but we can steering clear of their perjury citations. The crucial fact is that accused(s) were technically married in New York, for immigration purposes, and they were accused of a 1001 violation for having indicated that they were married. Part of the government's case was that such a marriage is not valid, and the court rejected that conclusion. The government's second prong was to maintain that the court "should affirm appellant's convictions on a theory of concealment", and this too the court rejected, saying "proof of their ulterior motives in marriage would not be tantamount to proof of willful and knowing concealment of these material facts". What they said on the forms was literally true, and they did not have a duty to volunteer information that they probably knew the government was interested in.

Contrarily in a later case, US v. Zalman 870 F.2d 1047 we are told that

the underlying purpose of a marriage is a material fact which bears upon the validity of the marriage, and that any false or fraudulent misrepresentation regarding the actual purpose of a marriage in order to gain status as a resident of the United States can be punished under 18 U.S.C.A. § 1001

so you have to be more truthful than the literal truth standard.

There are also circumstances where there is an independent duty to give information, such as reporting income to the IRS. In US v. Hernando Ospina 798 F.2d 1570 the court maintained

It is clear that in order to support a section 1001 concealment conviction there must be a legal duty to disclose the facts the defendant was convicted of concealing

citing US v. Tobon-Builes 706 F.2d 1092, where again there was a legal duty to report "existence, origin, and transfer of approximately $185,200 in cash".

In other words, it is not clear what information you are allowed to not volunteer when asked a question in a federal matter.

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    Threatening an FBI agent and his family is a federal crime, so you certainly could be prosecuted for lying about breaking his window if the feds decided the window breaking was part of a threat rather than a neighborhood accident. Commented Mar 19, 2016 at 6:28
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    As to your example regarding a friend, if you have actual knowledge of a felony 18 USC § 4 makes it a felony for anyone to "conceals and does not as soon as possible make known the same to some judge or other person in civil or military authority under the United States...". This appears to make it your responsibility to proactively provide the information, even if not asked.
    – Makyen
    Commented Mar 19, 2016 at 12:19

Yes. 18 USC 1001:

(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.

The base offence level under the sentencing guidelines is 14, same as for perjury.

Incidentally, I have no idea where you got the idea it's legal to lie to a state cop. That can very well be obstruction of justice, also a crime. Don't lie to cops.

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    Did I say anywhere that I thought it was legal to lie to state cops?
    – phoog
    Commented Mar 19, 2016 at 3:49
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    @phoog This question, combined with your first paragraph, gives a very strong implication that you think it's legal.
    – cpast
    Commented Mar 19, 2016 at 3:57
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    Well I don't. I'm just interested in federal law at the moment.
    – phoog
    Commented Mar 19, 2016 at 4:02
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    Just to make a very important point regarding the last sentence of this answer. It should read Don't talk to cops; just say No thank you or thank you. That's it. Commented Jul 23, 2016 at 12:56

In America, it is a federal crime to lie to an FBI agent, however it is not criminal for an FBI agent to lie to you. In fact, it is common practice for them to do so in their pursuit of evidence.

In short, American citizens (the most incarcerated people in the world per capita) are held to a higher standard than the lands highest law enforcement.

Title 18, United States Code, Section 1001 makes it a crime to: 1) knowingly and willfully; 2) make any materially false, fictitious or fraudulent statement or representation; 3) in any matter within the jurisdiction of the executive, legislative or judicial branch of the United States. Your lie does not even have to be made directly to an employee of the national government as long as it is "within the jurisdiction" of the ever expanding federal bureaucracy. Though the falsehood must be "material" this requirement is met if the statement has the "natural tendency to influence or [is] capable of influencing, the decision of the decisionmaking body to which it is addressed." United States v. Gaudin , 515 U.S. 506, 510 (1995). (In other words, it is not necessary to show that your particular lie ever really influenced anyone.)

- Solomon L. Wisenberg

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