Numbers 35:31

27 and the avenger of blood finds him outside of his city of refuge and kills him, then the avenger will not be guilty of bloodshed

28 because the manslayer must remain in his city of refuge until the death of the high priest. Only after the death of the high priest may he return to the land he owns.

29 This will be a statutory ordinance for you for the generations to come, wherever you live.

30 If anyone kills a person, the murderer is to be put to death on the testimony of the witnesses. But no one is to be put to death based on the testimony of a lone witness.

31 You are not to accept a ransom for the life of a murderer who deserves to die; he must surely be put to death.

32 Nor should you accept a ransom for the person who flees to a city of refuge and allow him to return and live on his own land before the death of the high priest.

33 Do not pollute the land where you live, for bloodshed pollutes the land, and no atonement can be made for the land on which the blood is shed, except by the blood of the one who shed it.

34 Do not defile the land where you live and where I dwell. For I, the LORD, dwell among the Israelites.”

Read all of Numbers 35