Deuteronomy 21:1-8

If a dead body is found on the ground, this ground that GOD, your God, has given you, lying out in the open, and no one knows who killed him, your leaders and judges are to go out and measure the distance from the body to the nearest cities. The leaders and judges of the city that is nearest the corpse will then take a heifer that has never been used for work, never had a yoke on it. The leaders will take the heifer to a valley with a stream, a valley that has never been plowed or planted, and there break the neck of the heifer. The Levitical priests will then step up. GOD has chosen them to serve him in these matters by settling legal disputes and violent crimes and by pronouncing blessings in GOD’s name. Finally, all the leaders of that town that is nearest the body will wash their hands over the heifer that had its neck broken at the stream and say, “We didn’t kill this man and we didn’t see who did it. Purify your people Israel whom you redeemed, O GOD. Clear your people Israel from any guilt in this murder.”