Numbers 35:29-32

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

30If 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.

31You are not to accept a ransom for the life of a murderer who deserves to die; he must surely be put to death. 32Nor 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.