1. According to some poskim capital punishment is only the maximum penalty but a Noahide court may impose a lesser penalty (Chelkat Yoav Tanyana 14; Rabbi J. David Bleich, “Mishpat Mavet Bedenai Benai Noach,” Jubilee Volume in Honor of Rav Joseph D. Soloveitchik 1:193-208 (5754); Rav Aharon Soloveichik, “On Noachides”, Beis Yitzchak 19:335-338 (5747)).
2. According to Ramban a Noahide judge may refuse to try someone.
3. According to Ramban, Rabbenu Tam and Rav Hirsch Shimon and Levi were wrong.