Jehovah's Witnesses use these verses to justify their refusal to report or investigate incidents of child molestation unless two or three Jehovah's Witnesses have witnessed the event.
At the mouth of two witnesses, or three witnesses, shall he that is worthy of death be put to death; but at the mouth of one witness he shall not be put to death. Deuteronomy 17:6
One witness shall not rise up against a man for any iniquity, or for any sin, in any sin that he sinneth: at the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established. Deuteronomy 19:15
If thy brother shall trespass against thee, go and tell him his fault between thee and him alone: if he shall hear thee, thou hast gained thy brother. But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established. Matthew 18:15-16
Against an elder receive not an accusation, but before two or three witnesses. 1 Timothy 5:19
In the mouth of two or three witnesses shall every word be established. 2 Corinthians 13:1
If witnesses do not come forward (and they are discouraged from doing so since it would embarrass the organization), then the victim is told to be quiet about it -- or risk being disfellowshipped.