Albert Barnes on John 7:51

Doth our law, &c. The law required justice to be done, and gave every man the right to claim a fair and impartial trial, Lev 19:15,16, Ex 23:1,2, De 19:15,18. Their condemnation of Jesus was a violation of every rule of right. He was not arraigned; he was not heard in self-defence, and not a single witness was adduced. Nicodemus demanded that justice should be done, and that he should not be condemned until he had had a fair trial. Every man should be presumed innocent until he is proved to be guilty. This is a maxim of law, and a most just and proper precept in our judgments in private life.

(t) "Doth our law" De 17:8, Prov 18:13