Numbers 35:33-34

So you shall not pollute and defile the land in which you live; for [the shedding of innocent] blood pollutes and defiles the land. No atonement (expiation) can be made for the land for the [innocent] blood shed in it, except by the blood (execution) of him who shed it. You shall not defile the land in which you live, in the midst of which I live, for I, the Lord, live among the people of Israel.’ ”