Numbers 35:29-33

‘These things shall be a statutory ordinance for you throughout your generations in all your dwelling places.

‘If anyone kills a person, the murderer shall be put to death on the testimony of witnesses, but no person shall be put to death on the testimony of only one witness.

Moreover, you shall not accept a ransom for the life of a murderer who is condemned to death, but he must be put to death.

And you shall not accept a ransom for one who has fled to his city of refuge, so that he may return to live in the land before the death of the priest.

So you shall not defile the land in which you live; for blood defiles the land, and no atonement can be made for the land for the blood that is shed on it, except by the blood of the one who shed it.