Accept atonement, O LORD, for your people Israel, whom you have redeemed, and do not set the guilt of innocent blood in the midst of your people Israel, so that their blood guilt be atoned for.’
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
Be merciful, O Lord, to thy people Israel, whom thou hast redeemed,.... Out of Egyptian bondage, and claimed as his own; and therefore it is requested he would be favourable to them, and show them mercy, and not punish them for a sin they were entirely ignorant of, though done by some one among them, whom as yet they could not discover.
Be merciful, O LORD, unto thy people Israel, whom thou hast redeemed, and lay not innocent blood unto thy people of Israel's charge. And the blood shall be forgiven them. (c) This was the prayer, which the priests made in the audience of the people.