1339533_large_watermark_compPeople race away from the ruin as the World Trade Center's North Tower collapses. (Photo: Jose Jimenez/Primera Hora/Getty Images)
For the full photo collection, go to LIFE.com
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.