Deuteronomy 19:6, 12

lest the avenger of blood pursue the manslayer, while his heart is hot, and overtake him, because the way is long, and smite him mortally; whereas he was not worthy of death, inasmuch as he hated him not in time past.

then the elders of his city shall send and fetch him thence, and deliver him into the hand of the avenger of blood, that he may die.