Deuteronomy 21:2-4

2your elders and judges are to come out and measure the distance from the victim to the nearby cities.

3The elders of the city nearest to the victim are to get a young cow that has not been yoked or used for work.

4The elders of that city will bring the cow down to a continually flowing stream, to a place not tilled or sown, and they will break its neck there by the stream.