Numbers 35:33

So ye shall not pollute the land wherein ye are,.... The land of Canaan, as it had been by the old inhabitants of it, by idolatry, adultery, and murder:

for blood it defileth the land: the shedding of innocent blood defiles a nation, and the inhabitants of it, brings guilt thereon, and subjects to punishment:

and the land cannot be cleansed of the blood that is shed therein, but by the blood of him that shed it; or "there can be no expiation" b, or "atonement made" for it in any other way; the blood of the murderer is required at his hands, and nothing short of it will satisfy law and justice, see Genesis 9:6.

b לא יכפר "non posset expiatio", Junius Tremellius, Piscator to the same sense Pagninus, Montanus, Tigurine version.