(B) is correct.

Issue: When can mistake of law be a defense to a crime?

Rule: Generally, mistake of law is not a defense, even though a defendant may not believe that their acts were criminal or that the mistake they made was reasonable. There are, however, exceptions to this rule. They are: (i) the defendant cannot be criminally responsible for actions taken at the advice of a public official; (ii) while acting on the erroneous advice of an attorney is not a defense, acting in reasonable reliance on an attorney may negate an otherwise necessary mental state element of the crime; (iii) the statute addressing such conduct was not made reasonably available before the defendant committed the criminal act; and (iv) the defendant reasonably relied on an official interpretation of the statute (only some states recognize this exception). Analysis: Here, three of the alternatives accurately reflect the exceptions that allow mistake of law to operate as a valid defense. However, the mistake of law in alternative (B) would not be a valid defense. Reliance on the erroneous advice of an attorney is not one of the exceptions that allows a mistake of law to operate as a defense. Importantly note the distinction between erroneous advice leading to a mistake of law, and erroneous advice that negates the requisite mental state for the particular charge.

(B) is correct because reliance on erroneous attorney advice is not a defense unless the advice prevents the individual from having the required mental state.

(A) is incorrect because reliance on the advice of a public official is a defense.

(C) is incorrect because the reliance on attorney advice here prevented the defendant from having the required mental state. Note here that we are dealing with criminal trespass, not the tort of trespass. In the tort of trespass, one will be liable if they intentionally enter the property, regardless of whether they knew it belonged to another or not and regardless of whether they thought it was legal or illegal. Criminal trespass on the other hand typically (like the statute in this example) requires that the defendant enter another’s property without permission knowingly and willfully.

(D) is incorrect because the statute addressing the conduct was not reasonably made available to the public.