Deuteronomy 19:10-13

10lest innocent blood be shed in your land that the Lord your God is giving you for an inheritance, and so the guilt of bloodshed be upon you.

11"But if anyone hates his neighbor and lies in wait for him and attacks him and strikes him fatally so that he dies, and he flees into one of these cities,

12then the elders of his city shall send and take him from there, and hand him over to the avenger of blood, so that he may die.

13Your eye shall not pity him, but you shall purge the guilt of innocent blood from Israel, so that it may be well with you.