Generally, where a particular fact is an element of the crime, it is no defense that the perpetrator is unaware of the existence of that fact, or had a mistaken belief about that fact. However, there are cases in which the courts have taken a different approach, either leaving the question of the effect of mistake open or recognizing mistake as justification or defense.
A person charged with kidnapping is entitled to introduce evidence to show that s/he believed s/he was acting under the authority of law, in a jurisdiction which allows the defense of mistake.