Deuteronomy 19:15
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. 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.
A charge of wrongdoing against a person is not established by one person's accusation alone, but only by the testimony of two or three witnesses. This requirement governs how wrongdoing is to be addressed in the church, guarding against accusations and reports being spread without proper witnesses. At Jesus' trial, the Roman officers objected that condemning Him to death on His own testimony was contrary to Jewish law, which demanded that a matter be established by two or three witnesses and not by one person's testimony alone.