Deuteronomy 21:1-9

“If someone is found slain, lying in the field, in the land which the LORD your God gives you to possess, and it is not known who has killed him, then your elders and judges shall go out and measure the distance to the cities which are around the dead person. It shall be that the elders of the city which is nearest to the dead man shall take a heifer of the herd, one which has not been worked and which has not pulled in a yoke; and the elders of that city shall bring the heifer down to a [river] valley with running water, which has not been plowed or planted, and shall break the heifer’s neck there in the valley. Then the priests, the sons of Levi, shall approach, for the LORD your God has chosen them to serve Him and to bless in the Name (Presence) of the LORD; and every dispute and every assault (violent crime) shall be settled by them. All the elders of that city nearest to the dead man shall wash their hands over the heifer whose neck was broken in the valley; and they shall respond, and say, ‘Our hands did not shed this blood, nor did our eyes see it. Forgive Your people Israel whom You have redeemed, O LORD, and do not put the guilt of innocent blood among Your people Israel.’ And the guilt of blood shall be forgiven them. So shall you remove the guilt of innocent blood from among you, when you do what is right in the sight of the LORD.