The LORD spoke to Moses in the plains of Moab by the Jordan at Jericho, saying, “Command the people of Israel to give to the Levites some of the inheritance of their possession as cities for them to dwell in. And you shall give to the Levites pasturelands around the cities. The cities shall be theirs to dwell in, and their pasturelands shall be for their cattle and for their livestock and for all their beasts. The pasturelands of the cities, which you shall give to the Levites, shall reach from the wall of the city outward a thousand cubits all around. And you shall measure, outside the city, on the east side two thousand cubits, and on the south side two thousand cubits, and on the west side two thousand cubits, and on the north side two thousand cubits, the city being in the middle. This shall belong to them as pastureland for their cities.
“The cities that you give to the Levites shall be the six cities of refuge, where you shall permit the manslayer to flee, and in addition to them you shall give forty-two cities. All the cities that you give to the Levites shall be forty-eight, with their pasturelands. And as for the cities that you shall give from the possession of the people of Israel, from the larger tribes you shall take many, and from the smaller tribes you shall take few; each, in proportion to the inheritance that it inherits, shall give of its cities to the Levites.”
And the LORD spoke to Moses, saying, “Speak to the people of Israel and say to them, When you cross the Jordan into the land of Canaan, then you shall select cities to be cities of refuge for you, that the manslayer who kills any person without intent may flee there. The cities shall be for you a refuge from the avenger, that the manslayer may not die until he stands before the congregation for judgment. And the cities that you give shall be your six cities of refuge. You shall give three cities beyond the Jordan, and three cities in the land of Canaan, to be cities of refuge. These six cities shall be for refuge for the people of Israel, and for the stranger and for the sojourner among them, that anyone who kills any person without intent may flee there.
“But if he struck him down with an iron object, so that he died, he is a murderer. The murderer shall be put to death. And if he struck him down with a stone tool that could cause death, and he died, he is a murderer. The murderer shall be put to death. Or if he struck him down with a wooden tool that could cause death, and he died, he is a murderer. The murderer shall be put to death. The avenger of blood shall himself put the murderer to death; when he meets him, he shall put him to death. And if he pushed him out of hatred or hurled something at him, lying in wait, so that he died, or in enmity struck him down with his hand, so that he died, then he who struck the blow shall be put to death. He is a murderer. The avenger of blood shall put the murderer to death when he meets him.
“But if he pushed him suddenly without enmity, or hurled anything on him without lying in wait or used a stone that could cause death, and without seeing him dropped it on him, so that he died, though he was not his enemy and did not seek his harm, then the congregation shall judge between the manslayer and the avenger of blood, in accordance with these rules. And the congregation shall rescue the manslayer from the hand of the avenger of blood, and the congregation shall restore him to his city of refuge to which he had fled, and he shall live in it until the death of the high priest who was anointed with the holy oil. But if the manslayer shall at any time go beyond the boundaries of his city of refuge to which he fled, and the avenger of blood finds him outside the boundaries of his city of refuge, and the avenger of blood kills the manslayer, he shall not be guilty of blood. For he must remain in his city of refuge until the death of the high priest, but after the death of the high priest the manslayer may return to the land of his possession. And these things shall be for a statute and rule for you throughout your generations in all your dwelling places.
“If anyone kills a person, the murderer shall be put to death on the evidence of witnesses. But no person shall be put to death on the testimony of one witness. Moreover, you shall accept no ransom for the life of a murderer, who is guilty of death, but he shall be put to death. And you shall accept no ransom for him who has fled to his city of refuge, that he may return to dwell in the land before the death of the high priest. You shall not pollute the land in which you live, for blood pollutes the land, and no atonement can be made for the land for the blood that is shed in it, except by the blood of the one who shed it. You shall not defile the land in which you live, in the midst of which I dwell, for I the LORD dwell in the midst of the people of Israel.” (Numbers 35:1-34 ESV)
The Levites do not inherit land in Israel, but instead are given pasture land around the cities designated by Israel, 48 in all. Six of these cities are cities of refuge where someone who kills another without malice aforethought may flee for protection from the dead person’s relative. Instead of a police force for such things, the relative of someone murdered was expected to take vengeance on the murderer. But there had to be at least two witnesses to convict someone of murder and if it was deemed manslaughter instead of first degree murder, the manslayer was to live in the city of refuge until the high priest at the time died. This was his penalty.
God required the death of a 1st degree murderer, however, in order to atone for the blood spilled in His land. Only the death of the killer kept the land from being defiled. Yahweh dwelled in the land among His people and there would be repercussions for defiling the land.
Yahweh dwells among us, His church, as well. His holy presence requires a reciprocal holiness on our part and a readiness to deal with our failures in regard to holiness. Paul says we are capable of judging such cases among us (1 Corinthians 6) and applying discipline correctly. Jesus told us that where two or three agree on any discipline it will be done in heaven (Matthew 18:15ff).