Brief for the National Association of Criminal Defense Lawyers the Cato Institute, the American Civil Liberties Union, and the American Civil Liberties Union of North Carolina as Amici Curiae in Support of Petitioner.

Argument: The North Carolina Supreme Court’s rule condoning traffic stops based on suspicion of perfectly lawful conduct ignores fundamental differences between mistakes of fact and mistakes of law. Treating mistakes of fact and law ‘the same’ under the Fourth Amendment contravenes well-established legal doctrine. There are important practical distinctions between mistakes of fact and mistakes of law. The North Carolina rule would have negative consequences for both individual citizens and law enforcement. The North Carolina Supreme Court’s rule will have negative consequences for individual liberty and will undermine law enforcement.

Brief for the National Association of Criminal Defense Lawyers as Amicus Curiae in Support of Petitioner.

Argument: Certiorari is warranted here based upon the entrenched, irreconcilable division among the federal courts of appeals and state courts of last resort on the question of whether a law enforcement officer’s reasonable mistake of law can provide the individualized suspicion that the Fourth Amendment requires to justify an investigatory stop. The North Carolina Supreme Court’s rule is flatly inconsistent with the principles underlying this Court’s Fourth Amendment jurisprudence. It has always been the province of the courts, not law enforcement, to determine and apply the law governing an investigatory stop. There is no basis under the Fourth Amendment for officers to conduct seizures based on nothing more than suspicion of conduct that violates no law. Second, the North Carolina Supreme Court’s rule, if left undisturbed, will have substantial negative effects, including condoning a broad swath of searches unrelated to suspicion of any violation of any actual law, and reducing or removing important incentives for police officers to understand thoroughly the laws they are charged with enforcing.

Brief in Support of Appellant by Amicus Curiae National Association of Criminal Defense Lawyers.

Argument: The trial court erred in barring the defense from introducing evidence to support the basis for the legal opinion Mathis gave to his client. Ambiguity in the statute with regard to mens rea requires the court to insert an appropriate state of mind element. The "knowledge" element of an offense occasionally includes knowledge of a legal "fact." The trial court improperly removed the mens rea element in this case. In the alternative, a mistake of law defense was appropriate in this case. Denying Mathis the right to present this evidence resulted in the denial of his right to present a defense.