Deuteronomy 19:10-12

so that innocent blood will not be shed [by blood avengers] in your land which the LORD your God is giving you as an inheritance, and blood guilt will not be on you [for the death of an innocent man]. “But if there is a man who hates his neighbor and lies in wait and ambush for him and attacks him and strikes him down so that he dies, and the assailant escapes to one of these cities, then the elders of his own city shall send for him and have him taken back from there and turn him over to the avenger of blood, so that he may be put to death.