Numbers 35:29-32

29These instructions will be a statutory ordinance for you throughout your generations wherever you live.

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

31You are not to accept a ransom for the life of someone who is guilty of murder; he must be put to death.

32Neither should you accept a ransom for the person who flees to his city of refuge, allowing him to return and live in the land before the death of the high priest.