Deuteronomy 19:10-13

10Then innocent blood will not be shed within your land that Adonai your God is giving you as an inheritance, and there would be blood upon you.

11“But suppose someone hates his neighbor, waits in hiding for him, rises up against him, strikes him dead, then flees to one of these cities.

12Then the elders of his hometown should send and take him from there and hand him over to the avenger of blood, to die.

13Your eye should not pity him, but you must purge the innocent blood from Israel, so that it may go well with you.