Matthew Poole and continuators on Numbers 35:33

33 So ye shall not pollute the land, wherein ye are: for blood, it defileth the land: and the land cannot be cleansed of the blood that is shed therein, but by the blood of him that sheddeth it .

These words are added as a reason not of the last Law ver. 32. for in that case the land was cleansed without the blood of the man-slayer, but of the Law next foregoing that verse 31. in which case it holds, and the sense is, if you shall spare the murderer or take any satisfaction for him, you do together with your selves involve your Land and People in guilt, and will certainly bring down Gods vengeance upon your selves and them.

Marginal references: Mic. 4. 11.; Heb. there can be no expiation for the land.