The Hands were Washed in Token of Innocency

Then all the elders of the city nearest the victim shall wash their hands by the stream over the heifer whose neck has been broken,

…and they shall declare, “Our hands did not shed this blood, nor did our eyes see it.

When Pilate saw that he was accomplishing nothing, but that instead a riot was breaking out, he took water and washed his hands before the crowd. “I am innocent of this man’s blood,” he said. “You bear the responsibility.”