Also known as: mistake-of-law defense · mistake of law · mistakes of law · ignorantia juris · ignorance of law
Written by attorneys · grounded in primary & secondary sources — see below
A defense in criminal prosecutions that excuses liability when a defendant's mistaken belief about the law negates the required mental state for an offense or when the defendant reasonably relied on an official statement of law later determined to be erroneous. The defense also applies when a criminal enactment was not known to the actor and had not been published or otherwise reasonably made available before the conduct. In tort, a parallel rule provides that a mistaken belief about legal rights does not relieve an actor of liability for trespass to chattels or conversion.
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Maria Morales repossessed a delivery van from a defaulting customer after consulting an outdated statute that she believed granted her an immediate right to seize the vehicle without court process. The statute had been amended months earlier to require judicial approval. Morales's sincere but mistaken belief about the governing law did not prevent the customer from recovering damages for conversion of the van.
Mason McCarthy, a self-employed contractor, stopped withholding federal income taxes after studying several court decisions and concluding that wages were not taxable income under the Sixteenth Amendment. The jury accepted that McCarthy's beliefs were sincere even though objectively unreasonable. Because the tax statute required proof of willfulness, the mistake-of-law defense prevented conviction.
Melanie Morris, a federal agent, obtained a warrant that mistakenly described the items to be seized as firearms rather than the actual target of drug records. She executed the warrant in good faith reliance on the magistrate's approval. The mistake of law regarding the warrant's facial validity did not support qualified immunity in the subsequent civil action.
Mariam Mansour made repeated bank deposits just under $10,000 to avoid paperwork after her accountant assured her that the structuring statute applied only to drug proceeds. The Supreme Court held that the government must prove she knew the structuring itself was illegal. Her mistake about the legal prohibition defeated the willfulness element.
Matthew Martinez possessed a semiautomatic rifle after receiving a written opinion from a licensed firearms dealer stating that the weapon fell outside the National Firearms Act's registration requirement. The Court required the government to prove Martinez knew of the registration duty. His good-faith mistake about the statute's scope negated the mens rea element.
Miguel Mendoza, a corrections officer, carried a firearm while off duty after reading the penal code exemption for peace officers and concluding it covered his position. The statute in fact excluded corrections officers from the exemption. Because the mistake concerned the legal scope of the defense rather than a fact, the court rejected the mistake-of-law claim and affirmed the conviction.
The defense is available when a defendant reasonably relies on an official statement of law contained in a statute, administrative order, or interpretation by the public officer or body charged with administering the law, and that statement is later determined to be erroneous. The reliance must produce a belief that the conduct is lawful, and the mistake must negate the required mental state or be expressly recognized by the governing law as exculpatory.
Yes, under the Model Penal Code approach a belief that conduct is not criminal is a defense when the enactment was not known to the actor and had not been published or otherwise reasonably made available before the conduct. The defense requires proof by a preponderance that the defendant lacked actual knowledge and that the government failed to provide reasonable notice.
…188, 191-193 (CA1 1985), we granted certiorari, 493 U. S. 1068 (1990). II The general rule that ignorance of the law or a mistake of law is no defense to criminal prosecution is deeply rooted in the American legal system. See, e. g. , United States v. Smith , 5 Wheat. 153, 182 (1820) (Livingston, J., dissenting); Barlow…
…of law." Ibid. In reversing the order, Justice Holmes stated the following for the Court: "It certainly is true that mere mistakes of law
…law. See, e. g. , Creighton, supra . Our qualified immunity doctrine applies regardless of whether the officer's error is a mistake of law
…“ ‘will not be disturbed [on appeal] unless there is an abuse of [the trial court’s] discretion . or unless there is a clear mistake of law
…duties reasonably. The protection of qualified immunity applies regardless of whether the government official’s error is “a mistake of law
A genuine and reasonable mistake about whether an item is legally controlled or whether conduct falls within a statutory exemption can negate the knowledge element when the offense requires awareness of that legal status. The defense succeeds if the mistake prevents the prosecution from proving the required culpable mental state beyond a reasonable doubt.
No, the defense requires reliance on an official statement from a governmental source charged with interpreting or enforcing the law. An anonymous online post or advice from a private party does not qualify, even if the defendant sincerely believed it, because the law does not recognize such sources as creating an exculpatory mistake of law.