Sforno on Deuteronomy 17:12/ספורנו על דברים י״ז:י״ב

1והאיש אשר יעשה בזדון, who deliberately hands down a ruling to be applied forthwith, which is against that handed down by the Supreme Court, ומת האיש ההוא, he is to be executed at the behest of the Supreme Court, and thereby all the people will hear about it and the absolute authority of the Sanhedrin will be preserved and the people will remain in awe of it.