Or HaChaim on Genesis 50:19/אור החיים על בראשית נ׳:י״ט

1 כי התחת אלוקים אני, "Am I then in G'd's place?" Joseph meant: "if you are guilty it is up to G'd to punish you; it is not up to me to revenge myself or to hold a grudge against you." Joseph may not have told the brothers that he had forgiven them because under Noachide law the matter did not depend on his forgiveness at all. Under Noachide law, once a person has committed the sin of kidnapping or robbery, he is guilty of the death penalty. The fact that the victim forgave the criminal is irrelevant to the penalty. Joseph added that he had to interpret the brothers' actions in a manner which reflected credit upon them.