This legal defense is embedded in US jurisprudence. Most people would be familiar with the concept of "mistake of law" not being a lawful defense. In other wo

This legal defense is embedded in US jurisprudence. Most people would be familiar with the concept of "mistake of law" not being a lawful defense. In other words, it is not a recognized defense to say one did the act, but should not be accountable because they did not know it was criminal. However, one exception is if a government official gives a interpretation of the law, even if that interpretation is wrong, then relying on the government official's interpretation becomes a lawful defense. Therefore, it is a little different that the Nuremberg defense, as I understand it, where that defense is essentially claiming you were ordered by superiors to take an action that was unlawful. So the practical difference being in one case you know or believe what you are being commanded to do is criminal and the other case you are specifically informed by some government official with authority that the act you are being ordered to do is lawful.