Deuteronomy 19:10-12

So innocent blood will not be shed in the midst of your land which the LORD your God gives you as an inheritance, and bloodguiltiness be on you. “But if there is a man who hates his neighbor and lies in wait for him and rises up against him and strikes him so that he dies, and he flees to one of these cities, then the elders of his city shall send and take him from there and deliver him into the hand of the avenger of blood, that he may die.