Numbers 35:26-28

But if ever he goes outside the walls of the safe town where he had gone in flight, And the giver of punishment, meeting him outside the walls of the town, puts him to death, he will not be responsible for his blood: Because he had been ordered to keep inside the safe town till the death of the high priest: but after the death of the high priest the taker of life may come back to the place of his heritage.