(a) A person is not relieved of criminal liability for conduct because he engages in such conduct under a mistaken belief of fact or law unless such mistake negatives the existence of the mental state required by the offense.

    (b) A person is not relieved of criminal liability for conduct because he believes his conduct does not constitute an offense unless his belief is reasonable and

    (1)    The offense is defined by an administrative regulation or order which is not known to him and has not been published or otherwise made reasonably available to him, and he could not have acquired such knowledge by the exercise of due diligence pursuant to facts known to him; or

    (2)    He acts in a reasonable reliance upon an official statement of the law, afterward determined to be invalid or erroneous, contained in:

        a.    A statute or ordinance;

        b.    An opinion or order of an appellate court;

        c.    An official interpretation of the statute, regulation or order defining the offense made by a public official or agency legally authorized to interpret such statute, regulation or order.

    (c) The burden of injecting the issue of reasonable belief that conduct does not constitute an offense under subparagraphs (b)(l) and (2) of this section is on the defendant.

(Code 1964, § 7.565)

     State law reference(s)--Similar provisions, RSMo. § 562.031.