Numbers 35:33-34

So ye shall not pollute the land wherein ye are: for blood, it polluteth the land; and no expiation can be made for the land for the blood that is shed therein, but by the blood of him that shed it. And thou shalt not defile the land which ye inhabit, in the midst of which I dwell: for I, Jehovah, dwell in the midst of the children of Israel.