'Witnesses' in the Bible

At the mouth of two witnesses, or three witnesses, shall he that is to die be put to death: he shall not be put to death at the mouth of one witness.

The hands of the witnesses shall be first upon him to put him to death, and afterwards the hands of all the people; and thou shalt put evil away from thy midst.

One witness shall not rise up against a man for any iniquity, and for any sin, in any sin that he sinneth: at the mouth of two witnesses, or at the mouth of three witnesses, shall a matter be established.