Mormon inserts himself into this discourse. The Gadiantons are accusing Nephi. They specifically accuse him of being against law. We have no record of what Nephi said against any particular law, and it may be that the intent of law in this case is more like rule. Nephi is speaking against the corruptness of their rule, which comes through their application of law as judges.
In the midst of this accusation, however, Mormon finds it necessary to insert his editorial comment that Nephi was justified by God, even if he was contrary to the Gadiantons. Mormon is saying that although Nephi contradicted the laws of the Gadiantons, he is following the laws of God.