But that's the point. He claims he did not know the law. And "Ignorance is no excuse" assumes that a law is knowable. If a law is vaguely worded or if its existence is not publicized, then ignorance does become an excuse. If the State lists illegal activities on an "assault" rifle registration, and leaves that one law off the list, then he can argue that the law was hidden from him and thus was unknowable.
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