Numbers 35:31
31 Moreover, you shall accept no ransom for the life of a murderer, who is guilty of death, but he shall be put to death.
Numbers 35:33
33 You shall not mpollute the land in which you live, for blood mpollutes the land, and no atonement can be made for the land for the blood that is shed in it, except nby the blood of the one who shed it.