Ignorance of the law is ordinarily not an excuse for criminal law violations, except when a person makes a mistake of law because of a reasonable reliance upon an official interpretation of the law. Heien v. North Carolina created a mistake of law defense based upon an officer’s ignorance of the law, functionally carving out a new exception to the Fourth Amendment exclusionary rule. In Heien, an officer’s ignorance of the law caused him to stop a car based on his mistaken belief that the defendant had violated the requirement for two working brake lights. Even though the officer was wrong about the law, Heien held that an officer’s reasonable mistake of law may support reasonable articulable suspicion to justify an investigatory stop. Consequently, the evidence obtained as a result of the stop was admissible. By importing the mistake of law defense from criminal law to allow for police ignorance, Heien represents a significant departure from the Court’s good faith exception jurisprudence, which was previously justified on reasonable reliance. Moreover, it contradicts criminal law’s application of and policies underlying the mistake of law defense.

This Article analyzes five ways in which the Court’s mistake of law analogy in the Fourth Amendment context is incongruous with the criminal law mistake of law defense. First, the Court’s excusal of the officer’s ignorance of the law creates an asymmetry between officers and laypersons. Laypersons are not excused from their ignorance of the law, but the Court deviates from criminal law doctrine by allowing the officer, the very person’s whose duty is to apply the law, to assert such a defense. Second, the Heien Court’s injection of reasonableness in deciding whether an officer’s ignorance of the law or mistake of law should be excused contradicts criminal law, which does not take reasonableness into account. Third, criminal law permits a mistake of law defense only when the defendant has relied on an official interpretation of an official statement of the law, whereas the Court accepted the mistake of law claim when the officer relied merely on his personal interpretation of the law. Fourth, the Court ignores the fundamental differences between an officer’s assertion of the mistake of law defense to avoid exclusion and a defendant’s assertion to avoid criminal liability. Defendants are afforded the mistake of law defense because a criminal conviction would jeopardize their liberty, property, and reputation and they would suffer additional collateral consequences, including loss of employment, benefits, and voting rights. In contrast, an officer merely risks evidence being excluded. Fifth, the Court upends the rule of lenity by failing to identify any ambiguity in the law before interpreting the law in the officer’s favor. The rule of lenity ordinarily requires that ambiguous laws be interpreted in the defendant’s favor.