Shall wash their hands over the heifer - Washing the hands, in reference to such a subject as this, was a rite anciently used to signify that the persons thus washing were innocent of the crime in question. It was probably from the Jews that Pilate learned this symbolical method of expressing his innocence.

And all the elders of that city that are next unto the slain man,.... The whole court of judicature belonging to it, all the magistracy of it; even though there were an hundred of them, Maimonides (x) says:

shall wash their hands over the heifer that is beheaded in the valley: in token of their innocence, and this they did not only for themselves, but for the whole city, being the representatives of it; see Psalm 26:6. Some think that this is a confirmation of the sense embraced by some, that it was a strong stream to which the heifer was brought; and there might be a stream of water here, and a valley also; though it would be no great difficulty to get from the city, which was near, a sufficient quantity of water to wash the hands of the elders with. This may denote the purification of sin by the blood of Christ, when it is confessed over him; and shows that priests and elders, ministers of the word, as well as others, stand in need of it; and that even those concerned in the death of Christ shared in the benefits of it.

(x) Hilchot Rotzeach, c. 9. sect. 3.

The elders of the town were to wash their hands over the slain heifer, i.e., to cleanse themselves by this symbolical act from the suspicion of any guilt on the part of the inhabitants of the town in the murder that had been committed (cf. Psalm 26:6; Psalm 73:13; Matthew 27:24), and then answer (to the charge involved in what had taken place), and say, "Our hands have not shed this blood (on the singular שׁפכה, see Ewald, 317, a.), and our eyes have not seen" (sc., the shedding of blood), i.e., we have neither any part in the crime nor any knowledge of it: "grant forgiveness (lit., 'cover up,' viz., the blood-guiltiness) to Thy people...and give not innocent blood in the midst of Thy people Israel," i.e., lay not upon us the innocent blood that has been shed by imputation and punishment. "And the blood shall be forgiven them," i.e., the bloodshed or murder shall not be imputed to them. On נכּפּר, a mixed form from the Niphal and Hithpael, see Ges. 55, and Ewald, 132, c.

And all the elders of that city, that are next unto the slain man, shall wash their hands over the heifer that is beheaded in the valley:

21:1-9 If a murderer could not be found out, great solemnity is provided for putting away the guilt from the land, as an expression of dread and detesting of that sin. The providence of God has often wonderfully brought to light these hidden works of darkness, and the sin of the guilty has often strangely found them out. The dread of murder should be deeply impressed upon every heart, and all should join in detecting and punishing those who are guilty. The elders were to profess that they had not been any way aiding or abetting the sin. The priests were to pray to God for the country and nation, that God would be merciful. We must empty that measure by our prayers, which others are filling by their sins. All would be taught by this solemnity, to use the utmost care and diligence to prevent, discover, and punish murder. We may all learn from hence to take heed of partaking in other men's sins. And we have fellowship with the unfruitful works of darkness, if we do not reprove them.