2 witness rule is in the Bible. To protect the innocent.
Matthew 18:16: "…at the mouth of two or three witnesses every matter may be established."
2 Corinthians 13:1: “…At the mouth of two witnesses or of three every matter must be established."
1 Timothy 5:19 "Do not admit an accusation against an older man, except only on the evidence of two or three witnesses."
US Courts USED to follow this rule. We should put this in the revised Constitution as well.