Deuteronomy 19:9-11

9and if you keep all these commandments and do them, which I command you today, to love the Lord your God and to walk always in His ways, then you shall add three more cities for yourself besides these three,

10lest innocent blood be shed in the midst of your land which the Lord your God is giving you as an inheritance, and thus guilt of bloodshed be upon you.

11“But if anyone hates his neighbor, lies in wait for him, rises against him and strikes him mortally, so that he dies, and he flees to one of these cities,