They gathered the way crowds always do at the memorial — from the front, filling the rows nearest the wall first, then spilling back toward the avenue. By noon every square of the plaza was occupied. The police moved at two. They didn't charge — they kettled, pushing inward from all sides until the crowd compressed into the center two-by-two block, the rest of the plaza suddenly, eerily empty. The people in that tight knot couldn't move, couldn't leave, couldn't do anything but stand. By evening the cordon lifted and the crowd flowed back to fill the whole space, quieter than before.