John Calvin Commentary Deuteronomy 21:6

"And all the elders of that city, who are nearest unto the slain man, shall wash their hands over the heifer whose neck was broken in the valley;" — Deuteronomy 21:6 (ASV)

And all the elders of that city. The washing of their hands had the effect of further stirring them up, so that they would not rashly declare in that solemn rite that they were pure and guiltless. For it was as if they had presented the corpse of the dead man before God and had stood opposite it to purge the crime.

At the same time, they also ask for pardon, because the man might have been killed through their carelessness. And again, since the sacrilege of Achan alone contaminated the whole people, they feared that God's vengeance might spread further on account of the offense committed. Thus they are again taught how greatly God abominates murders, when the people pray to be pardoned for the crime of another, as if, merely by looking at it, they had contracted guilt.

God finally declares that He will not charge it to them when they have properly performed this rite of expiation. This is not because the heifer was the price of satisfaction to propitiate God, but because in this way they humbly reconciled themselves to Him and shut the door against future murders. For this reason it is said—You shall put away the blood from among you; for if the murder is overlooked, a stain remains on the people, and the earth itself, in a way, stinks before God.