NEW YORK, Sept 11: Americans commemorated 9/11 with solemn ceremonies and vows Wednesday to “never forget” 18 years after the deadliest terror attack on American soil.

WASHINGTON DC, Oct 14: Leslie Robertson, the lead structural engineer of the World Trade Center's infamous Twin Towers, was haunted by their collapse and the pain that followed 9/11.

IN PICTURES: 9/11 Twin Towers attack

September 11, 2018 13:15 pm

9/11 Twin Towers attack: How the day that changed the world unfolded

The last phone calls of plane passengers, crew and office workers killed on September 11 have been collected for posterity in New York. The recordings are devastating.