At 8:46 on the morning of Sept. 11, 2001, American Airlines Flight 11 struck the north face of 1 World Trade Center.

The plane’s impact sheared through the tower’s core, collapsing the stairwells and cutting the upper floors off from any route down. Five floors above the crash zone, on 101 through 105, sat the New York headquarters of Cantor Fitzgerald, the country’s dominant bond-trading firm.