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Two women hold each other as they watch the World Trade Center burn following a terrorist attack on the twin skyscrapers in New York Tuesday, Sept. 11, 2001. Terrorists crashed two planes into the World Trade Center and the twin 110-story towers collapsed Tuesday morning. (AP Photo/Ernesto Mora)

Confronting Terror: Faces of 9/11

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.