Deuteronomy 21:1-9

If one be found slain in the land which Jehovah thy God giveth thee to possess it, lying in the field, and it be not known who hath smitten him; then thy elders and thy judges shall come forth, and they shall measure unto the cities which are round about him that is slain: and it shall be, that the city which is nearest unto the slain man, even the elders of that city shall take a heifer of the herd, which hath not been wrought with, and which hath not drawn in the yoke; and the elders of that city shall bring down the heifer unto a valley with running water, which is neither plowed nor sown, and shall break the heifer’s neck there in the valley. And the priests the sons of Levi shall come near; for them Jehovah thy God hath chosen to minister unto him, and to bless in the name of Jehovah; and according to their word shall every controversy and every stroke be. And all the elders of that city, who are nearest unto the slain man, shall wash their hands over the heifer whose neck was broken in the valley; and they shall answer and say, Our hands have not shed this blood, neither have our eyes seen it. Forgive, O Jehovah, thy people Israel, whom thou hast redeemed, and suffer not innocent blood to remain in the midst of thy people Israel. And the blood shall be forgiven them. So shalt thou put away the innocent blood from the midst of thee, when thou shalt do that which is right in the eyes of Jehovah.