Say Bob was murdered at a coffee shop, and Jerry was a witness at the scene. At the trial, he is under oath, and gives his testimony. In his testimony, he explicitly claims that he was watching America's Funniest Home Videos up to the point when the murderer entered the shop.

Later in the trial, video evidence, while first and foremost showing that the defendant did indeed murder Bob, also showed that Jerry was watching something that wasn't America's Funniest Home Videos at the point when the murderer entered the shop. For the purpose of simplicity, let's assume that what he was watching is perfectly fine legally speaking. Let's also assume that he knowingly lied about what he was watching, and didn't make a simple mistake. Even though this detail was virtually irrelevant to his testimony, he still technically lied under oath, which is the definition of perjury.

Could this result in Jerry being criminally prosecuted and/or his entire testimony becoming invalid?

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    The exact program might be relevant if what Jerry was watching was on a TV channel, as opposed to VOD or streaming. The statement "I was watching America's Funniest Home Videos when the suspect entered the shop" could be a very relevant lie if America's Funniest Home Videos airs every Friday from 2pm to 3pm, whereas the program Jerry was actually watching airs every Friday from 3pm to 4pm.
    – Stef
    Commented Jan 22, 2023 at 17:12
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    Also, the falsity of this statement could be used to invalidate it. If Jerry is known to have been watching America's Funniest Home Videos at another time, then it could be argued that if he claims to have been watching America's Funniest Home Videos when the suspect entered, then he must be confusing those two times, and thus his testimony is not reliable. In your question you discard the "simple mistake" possibility, but it can't be discarded in reality: even if Jerry later claims to have been lying, there is no way to know for sure whether Jerry was lying or was making a mistake.
    – Stef
    Commented Jan 22, 2023 at 17:23
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    A lot of the speculation in comments around the relevance of airing times could easily have been avoided by including more details rather than hand-wave it away. For example, Jerry says that he was watching America’s Funniest Home Videos on YouTube, but in fact he was watching Keeping Up with the Kardashians on Netflix – he just didn’t want to admit that he likes watching the Kardashians, because he thinks it’s embarrassing. Commented Jan 24, 2023 at 13:10
  • Uh… Who would give a rat's whisker about what he was actually watching, in or of itself? If he claimed to be watching anything when he was not, or claimed not to be watching anything when in fact he was, either might be a problem. Please make more clear why there's a problem in your Question. Commented Jan 24, 2023 at 20:58

3 Answers 3


Take the US federal perjury statute as an example:

Whoever 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 ...

The key word is material, meaning relevant, important, essential. From your description, the specific show that Jerry was watching is not material to the proceeding in which the testimony was given, so Jerry has not perjured himself.

Other common law jurisdictions will likewise have materiality as an element of perjury.

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    What if Jerry was watching something illegal, and he was lying in his testimony to cover up his own crimes? Would that make his lies material?
    – nick012000
    Commented Jan 22, 2023 at 10:58
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    @nick012000 Wouldn't that be an unrelated crime and not relevant to the case on trial?
    – Joe W
    Commented Jan 22, 2023 at 15:28
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    The show could be material because they might need to verify that it was being shown at the time he claimed to be there. (Of course this doesn't apply if he's watching on-demand.)
    – Barmar
    Commented Jan 22, 2023 at 16:44
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    @nick012000 If that's the case he should refuse to answer on the basis of the 5th Amendment (or equivalent in other jurisdictions).
    – Barmar
    Commented Jan 22, 2023 at 16:45
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    If Tom and Jerry ran at 9:30 and Bugs Bunny at 10:00, then lying which one you watched could very well be material. For example if the murderer has a cast iron alibi for 10:00. If Tom and Jerry ran at 9:30 and you watched some porn that ran on a different channel at 9:30, less so. I'd recommend telling the truth, the legal risk is much higher than a bit of embarrassment in this case.
    – gnasher729
    Commented Jan 23, 2023 at 11:03

Section 1 Perjury Act 1911 says that:

(1) If any person lawfully sworn as a witness or as an interpreter in a judicial proceeding wilfully makes a statement material in that proceeding, which he knows to be false or does not believe to be true, he shall be guilty of perjury,

Therefore, just lying under oath is not enough to be guilty of perjury. The untruth must be shown to be "material" (which has the same meaning given in Nate's answer, i.e. relevant, important, essential).

That said, although Jerry does not appear to have committed perjury, the defence may consider using his untruths as a tactic to confuse or persuade the jury by questioning him under cross-examination as to why he lied in an attempt to discredit his testimony and allege he is not a witness of truth - and possibly also allege the police officer who took his initial statement was incompetent (or maybe corrupt) for not checking the facts. The defence argument could, with a bit of polish and refinement, go something like "the witness lied and the police are incompetent, so how can you trust the video evidence." Everyone likes a conspiracy theory!


As discussed in this article, it is well established that a conviction can be nullified if the testimony that it is based on is known by the prosecution to be false. The requirements imposed w.r.t. prosecution knowledge are not easy to satisfy. There is no evidence that the prosecution knew that the testimony was in part false, nor that it was material. Materiality is relevant, see US v. Bagley, which holds that

the prosecutor's failure to disclose evidence that could have been used effectively to impeach important Government witnesses requires automatic reversal. Such nondisclosure constitutes constitutional error and requires reversal of the conviction only if the evidence is material in the sense that its suppression might have affected the outcome of the trial.

As for prosecution for perjury, he can maybe be prosecuted for perjury, though given the facts in evidence he will not be convicted (so the answer about prosecution depends on how the gaps are filled in). Perjury statutes have three essential elements. First, the statement must be false – that much could be true, depending on what he said. If he said "I was watching America's Funniest Cat Videos at the time when Smith entered", and the other video showed that he was watching WTF Smackdown, the testimony would be false. If he said "I had been watching America's Funniest Cat Videos at the time when Smith entered", then the statement is false if he had not been watching Cat Vid at all prior to Smith's entry. See Bronston v. US for the "literal truth" requirement.

Second, the statement has to be material, not just false. We've covered this – there is nothing in evidence indicating that the statement is material. Third, the prosecution must prove that defendant knew that the statement is false. Although you stipulate a material fact, this is not possible in the real world – the prosecution cannot stipulate that the defense knows that the statement is false. They must introduce evidence proving that he knew that the statement is literally false. It's not possible to subpoena the contents of a person's mind, and without any evidence regarding knowledge, there can be no conviction. So, knowing all of this, the prosecution cannot prosecute him for perjury, until you change the scenario.

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