Numbers 35:12, 21, 24, 27

And the cities shall be unto you for refuge from the avenger, that the manslayer die not, until he stand before the congregation for judgment.

or in enmity smote him with his hand, so that he died; he that smote him shall surely be put to death; he is a murderer: the avenger of blood shall put the murderer to death, when he meeteth him.

then the congregation shall judge between the smiter and the avenger of blood according to these ordinances

and the avenger of blood find him without the border of his city of refuge, and the avenger of blood slay the manslayer; he shall not be guilty of blood