Deuteronomy 21:2-6

then your elders and your judges shall go out and measure the distance to the cities which are around the one who was killed.

And it shall be that the city which is nearest to the person killed, that is, that the elders of that city shall take a heifer of the herd that has not been worked and has not pulled in a yoke;

and the elders of that city shall bring the heifer down to a valley with running water, which has not been plowed or sown, and they shall break the heifer’s neck there in the valley.

Then the priests, the sons of Levi, shall come forward, because the Lord your God has chosen them to serve Him and to bless in the name of the Lord; and every dispute and violent crime shall be settled by them.

And all the elders of that city which is nearest to the person killed shall wash their hands over the heifer whose neck was broken in the valley;