Numbers 35:29

27and the avenger of blood finds him outside of the border of his city of refuge, and the avenger of blood kills the man slayer, he shall not be guilty of blood,

28because 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 man slayer shall return into the land of his possession.

29“‘These things shall be for a statute and ordinance to you throughout your generations in all your dwellings.

30“‘Whoever kills any person, the murderer shall be slain based on the testimony of witnesses; but one witness shall not testify alone against any person so that he dies.

31“‘Moreover you shall take no ransom for the life of a murderer who is guilty of death. He shall surely be put to death.