Numbers 35:33

33. Not pollute the land According to the conception of both Greeks and Hebrews an unavenged murder stained the land with guilt and exposed it to the most dreadful judgments. A government in sympathy with crime, or indifferent to the claims of justice, ought to feel the bolts of divine wrath.

Cannot be cleansed Literally, “and for the land atonement is not made except in the blood of him that murderously shed blood.” The atonement was not effected by the blood of the murderer as a sacrificial victim, but by the righteous conduct of the authorities and people in slaying him, and thus endeavoring to make murder odious. See the Greek tragedy, “OEdipus Rex.”