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Stunned, frightened Marcy Borders, 28, is covered in dust as she takes refuge in an office building after one of the World Trade Center towers collapsed. Borders was caught outside on the street as the cloud of smoke and dust enveloped the area, and raced into the building seeking shelter -- a building into which freelance photographer Stan Honda had also fled. "She was sort of this ghostly figure," Honda told LIFE.com, "covered in grey-white dust, and I thought that this was an amazing thing to see, that this would make an important picture of what was happening out there." Of all the images from 9/11, Honda's picture is perhaps the most immediate representation of the collective and individual shock felt by those who were actually there, in lower Manhattan, when the towers fell. (Photo: STAN HONDA/AFP/Getty Images)

For the full photo collection, go to LIFE.com

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.