Deuteronomy 19:11-13 NIV

11 But if out of hate someone lies in wait, assaults and kills a neighbor, and then flees to one of these cities,

References for Deuteronomy 19:11

12 the killer shall be sent for by the town elders, be brought back from the city, and be handed over to the avenger of blood to die.
13 Show no pity. You must purge from Israel the guilt of shedding innocent blood, so that it may go well with you.

References for Deuteronomy 19:13