Numbers 35:30

27 And the avenger of blood find him without the borders of the city of his refuge, and the avenger of blood shall kill the slayer; he shall not be guilty of blood:

28 Because he should have remained in the city of his refuge until the death of the high priest: but after the death of the high priest the slayer shall return into the land of his possession.

29 So these [things] shall be for a statute of judgment to you throughout your generations in all your dwellings.

30 Whoever 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.

31 Moreover, ye shall take no satisfaction for the life of a murderer, who [is] guilty of death: but he shall be surely put to death.

32 And ye shall take no satisfaction for him that hath fled to the city of his refuge, that he should 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 defileth the land: and the land cannot be cleansed of the blood that is shed in it, but by the blood of him that shed it.