17 A man that doeth violence to the blood of any person shall flee to the pit; let no man stay him.
This agrees with that ancient law, Whoso sheddeth man’s blood, by man shall his blood be shed (Gen. 9:6), and proclaims, 1. The doom of the shedder of blood. He that has committed murder, though he flees for his life, shall be continually haunted with terrors, shall himself flee to the pit, betray himself, and torment himself, like Cain, who, when he had killed his brother, became a fugitive and a vagabond, and trembled continually.
2. The duty of the avenger of blood, whether the magistrate or the next of kin, or whoever are concerned in making inquisition for blood, let them be close and vigorous in the prosecution, and let it not be bought off. Those that acquit the murderer, or do any thing to help him off, come in sharers in the guilt of blood; nor can the land be purged from blood but by the blood of him that shed it, Num. 35:33.
– Matthew Henry Commentary.