Numbers 35
31 Ref Further, no price may be given for the life of one who has taken life and whose right reward is death: he is certainly to be put to death.
32 Ref And no price may be offered for one who has gone in flight to a safe town, for the purpose of letting him come back to his place before the death of the high priest.
33 Ref So do not make the land where you are living unholy: for blood makes the land unholy: and there is no way of making the land free from the blood which has come on it, but only by the death of him who was the cause of it.