Deuteronomy 19:15

A single witness shall not suffice against a person for any crime or for any wrong in connection with any offense that he has committed . Only on the evidence of two witnesses or of three witnesses shall a charge be established .

One witness is not enough to convict anyone accused of any crime or offense they may have committed. A matter must be established by the testimony of two or three witnesses.

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.