RSA 626:3: Effect of Ignorance or Mistake.

I. A person is not relieved of criminal liability because he acts under a mistaken belief of fact unless:

(a) The mistake negatives the culpable mental state required for commission of the offense; or

(b) The statute defining the offense expressly provides that such mistake is a defense; or

(c) Such mistake supports a defense of justification as defined in RSA 627.

II. A person is not relieved of criminal liability because he acts under a mistaken belief that his conduct does not, as a matter of law, constitute an offense unless his belief is founded upon a statement of the law contained in a statute or other enactment, or an administrative order or grant of permission, or a judicial decision of a state or federal court, or a written interpretation of the law relating to the offense officially made by a public servant, agency or body legally empowered with authority to administer, enforce or interpret such law. The defendant must prove a defense arising under this subsection by a preponderance of evidence.