Numbers 35:30

27 and the avenger of blood find him without the border of his city of refuge, and the avenger of blood slay the manslayer; he shall not be guilty of blood,

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

29 And these things shall be for a statute [and] ordinance unto you throughout your generations in all your dwellings.

30 Whoso killeth any person, the murderer shall be slain at the mouth of witnesses: but one witness shall not testify against any person that he die.

31 Moreover ye shall take no ransom for the life of a murderer, that is guilty of death; but he shall surely be put to death.

32 And ye shall take no ransom for him that is 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 wherein ye are: for blood, it polluteth the land; and no expiation can be made for the land for the blood that is shed therein, but by the blood of him that shed it.