Albert Barnes on Matthew 27:24

He took water, etc. The Jews were accustomed to wash their hands when they wished to show that they were innocent of a crime committed by others. See De 21:6, Ps 26:6. They often used signs to represent their meaning. Pilate, in doing this, meant to denote that they were guilty of his death, but that he was innocent. But the mere washing of his hands did not free him from guilt, he was bound as a magistrate to free an innocent man; and whatever might be the clamour of the Jews, he was guilty at the bar of God for suffering the holy Saviour to be led to execution, to gratify the malice of enraged priests, and the clamours of a tumultuous populace.

See ye to it. That is, take it upon yourselves. Ye are responsible for it, if ye put him to death.

(x) "his hands" De 21:6