Deuteronomy 19:9-11

9if thou shalt keep all this commandment to do it, which I command thee this day, to love Jehovah thy God, and to walk ever in his ways; then shalt thou add three cities more for thee, besides these three: 10that innocent blood be not shed in the midst of thy land, which Jehovah thy God giveth thee for an inheritance, and so blood be upon thee.

11But if any man hate his neighbor, and lie in wait for him, and rise up against him, and smite him mortally so that he dieth, and he flee into one of these cities;