Deuteronomy 21:1

"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,

Surrounding context

21:1 "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,

21:2 then your elders and your judges shall go out and measure the distance from the slain man to the surrounding cities.