Deuteronomy 19:6, 12

otherwise the avenger of blood might pursue the manslayer in the heat of his anger, and overtake him, because the way is long, and take his life, though he was not deserving of death, since he had not hated him previously.

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.