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People in front of New York's St. Patrick's Cathedral react with horror as they look down Fifth Ave towards the World Trade Center towers after planes crashed into their upper floors Tuesday morning, Sept. 11, 2001. Explosions and fires collapsed the 110-story buildings. (AP Photo/Marty Lederhandler)

Confronting Terror: Faces of 9/11

January 1, 1970

Among the most eloquent and unsettling of the countless photographs from September 11, 2011, are those focusing not on the fall of the towers, or the jagged, smoking hole in the Pentagon, but on faces. Human faces etched with shock, fear, and disbelief at the cataclysm unfolding above them, or staring glassy-eyed into some unseen distance, stunned by the enormity of the barbarous terror unleashed that cloudless, late-summer morning. Here, LIFE.com presents a gallery focusing on witnesses to terror as they confront the unspeakable.