And the elders of that city shall bring down the heifer unto a rough valley, which is neither eared nor sown, and shall strike off the heifer’s neck there in the valley:
Care had been taken by some preceding laws for the vigorous and effectual persecution of a wilful murderer (Deu 19:11 etc.), the putting of whom to death was the putting away of the guilt of blood from the land; but if this could not be done, the murderer not being discovered, they must not think that the land was in no danger of contracting any...
Commenting on Deuteronomy 21:1-9
The elders of that city shall bring down the heifer unto a rough valley,.... Cities being generally built on hills, and so had adjacent valleys, to which there was a descent; but here a rough valley, or the rougher part of it, was selected for this purpose.
And the elders of that city shall bring down the heifer unto a rough valley, which is neither eared nor sown, and shall strike off the heifer's neck there in the valley: (b) That the blood shed of the innocent beasts in a solitary place, might make them abhor the fact.