Sforno on Deuteronomy 17:6/ספורנו על דברים י״ז:ו׳

1על פי שנים עדים או שלושה, even if the charge is idolatry, the entire testimony is disqualified if one of the witnesses is found to be inadmissible. We do not rule that seeing there are a sufficient number of reliable and legally admissible witnesses left, we proceed with the trial on that basis.