Deuteronomy 19:11-13

11 But if someone at enmity with another lies in wait and attacks and takes the life of that person, and flees into one of these cities,
12 then the elders of the killer's city shall send to have the culprit taken from there and handed over to the avenger of blood to be put to death.
13 Show no pity; you shall purge the guilt of innocent blood from Israel, so that it may go well with you.
New Revised Standard Version Bible, copyright 1989, Division of Christian Education of the National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved.