Numbers 35:26-28

26But if the slayer at any time goes outside the boundary of the town to which he had fled,

27and the avenger of blood finds him outside the borders of the town of refuge, and the avenger of blood kills the slayer, he will not be guilty of blood,

28because the slayer should have stayed in his town of refuge until the death of the high priest. But after the death of the high priest, the slayer may return to the land of his possessions.