Numbers 35:30-33

ACV(i) 30 Whoever kills any person, the murderer shall be slain at the mouth of witnesses, but one witness shall not testify against any person so that he dies. 31 Moreover ye shall take no ransom for the life of a murderer who is guilty of death, but he shall surely be put to death. 32 And ye shall take no ransom for him who has fled to his city of refuge, that he may come again to dwell in the land, until the death of the priest. 33 So ye shall not pollute the land in which ye are, for blood, it pollutes the land. And no expiation can be made for the land for the blood that is shed in it, but by the blood of him who shed it.