Numbers 35:29-32

29So these things must be a statutory ordinance for you throughout your generations, in all the places where you live.

30“Whoever kills any person, the murderer must be put to death by the testimony of witnesses; but one witness cannot testify against any person to cause him to be put to death.

31Moreover, you must not accept a ransom for the life of a murderer who is guilty of death; he must surely be put to death.

32And you must not accept a ransom for anyone who has fled to a town of refuge, to allow him to return home and live on his own land before the death of the high priest.