Deuteronomy 21:1-9

“If anyone is found slain, lying in the field in the land which the LORD your God is giving you to possess, and it is not known who killed him, then your elders and your judges shall go out and measure the distance from the slain man to the surrounding cities. And it shall be that the elders of the city nearest to the slain man will take a heifer which has not been worked and which has not pulled with a yoke. The elders of that city shall bring the heifer down to a valley with flowing water, which is neither plowed nor sown, and they shall break the heifer’s neck there in the valley. Then the priests, the sons of Levi, shall come near, for the LORD your God has chosen them to minister to Him and to bless in the name of the LORD; by their word every controversy and every assault shall be settled. And all the elders of that city nearest to the slain man shall wash their hands over the heifer whose neck was broken in the valley. Then they shall answer and say, ‘Our hands have not shed this blood, nor have our eyes seen it. Provide atonement, O LORD, for Your people Israel, whom You have redeemed, and do not lay innocent blood to the charge of Your people Israel.’ And atonement shall be provided on their behalf for the blood. So you shall put away the guilt of innocent blood from among you when you do what is right in the sight of the LORD.