D'varim (Deuteronomy)13:9(8)
Lo-toveh lo velo tishma elav velo-tachos eynecha alav velo-tachmol velo-techaseh alav.
Do not agree with him, and do not listen to him. Do not let your eyes pity him, do not show him any mercy, and do not try to cover up for him

The traditional view says that the faithful is not allowed to justify what the Maysit, the misleader to idols is trying to do. Additionally, the faithful is forbidden to plead for the Maysit in court, even if he knows of something that can be said in favor of the Maysit.

I believe that this matter would be the same as the city caught up in idolatry. The matter would have to be proved. "Then shall you inquire, and make search, and ask diligently; and, behold, if it be truth, and the thing certain, that such abomination is done in the midst of you" (Devarim/Deuteronomy 13:15[14])

1 Timothy 5:19-20
Don’t receive an accusation against an elder, except at the word of two or three witnesses. Rebuke before the whole assembly those leaders who continue sinning, as a warning to the others.

The point is that we must let the justice of YHVH be done. We must not allow that justice to be hindered.

Shalom v'brakhot
Chezek Shlomo

Be libi tzavanti imratecha le ma'an lo echta lach.
(Tehillim 119:11)