Numbers 35:30-33

30Before you kill a murderer, people must agree that they saw him kill someone. But if only one person saw what happened, that is not enough for you to kill him.

31You must not accept money to pay for the life of a murderer. If he is guilty of murder, you must kill him.

32Also, you must not accept money from a killer who has run to a safe city. You must not let him return to his own home until the leader of the priests has died.

33Murder causes the land where you live to become unclean. You have to make it clean again. You must kill anyone who murders another person. That is the only way to make the land clean again.