Two members of the New York City Fire Department look through the open ceiling of the Oculus, part of the World Trade Center transportation hub in New York on Tuesday. The transit hall ceiling window was opened just before 10:28 a.m., marking the moment that the North Tower of the World Trade Center collapsed on Sept. 11, 2001.

Two members of the New York City Fire Department look through the open ceiling of the Oculus, part of the World Trade Center transportation hub in New York on Tuesday. The transit hall ceiling window was opened just before 10:28 a.m., marking the moment that the North Tower of the World Trade Center collapsed on Sept. 11, 2001.