Deuteronomy 19:15-21

A single witness shall not rise up against a man on account of any iniquity or any sin which he has committed; on the evidence of two or three witnesses a matter shall be confirmed.

If a malicious witness rises up against a man to accuse him of wrongdoing, then both the men who have the dispute shall stand before the LORD, before the priests and the judges who will be in office in those days.

The judges shall investigate thoroughly, and if the witness is a false witness and he has accused his brother falsely, then you shall do to him just as he had intended to do to his brother.

Thus you shall purge the evil from among you. The rest will hear and be afraid, and will never again do such an evil thing among you.

Thus you shall not show pity: life for life, eye for eye, tooth for tooth, hand for hand, foot for foot.