Numbers 35:30-34

³⁰Whoso killeth any person, the murderer shall be put to death by the mouth of witnesses: but one witness shall not testify against any person to cause him to die. ³¹Moreover ye shall take no satisfaction for the life of a murderer, which is guilty of death: but he shall be surely put to death. ³²And ye shall take no satisfaction for him that is fled to the city of his refuge, that he should come again to dwell in the land, until the death of the priest. ³³So ye shall not pollute the land wherein ye are: for blood it defileth the land: and the land cannot be cleansed of the blood that is shed therein, but by the blood of him that shed it. ³⁴Defile not therefore the land which ye shall inhabit, wherein I dwell: for I the LORD dwell among the children of Israel.