'Witnesses' in the Bible

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

The hand of the witnesses shall be first on him to put him to death, and afterward the hand of all the people. So you shall put away the evil from the midst of you.

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