Deuteronomy 19:10-12

lest innocent blood be shed in the midst of your land which the LORD your God is giving you as an inheritance, and thus guilt of bloodshed be upon you. “But if anyone hates his neighbor, lies in wait for him, rises against him and strikes him mortally, so that he dies, and he flees to one of these cities, then the elders of his city shall send and bring him from there, and deliver him over to the hand of the avenger of blood, that he may die.