For Tim Duffy, the day started with a postcard-perfect sky over Cape Cod. Within hours, everything changed.
From his jet fighter, Duffy had a ghastly bird's-eye view of lower Manhattan, watching the second tower of the World Trade Center collapse beneath him.
"Anytime I see it's a beautiful day to fly, I kind of think of that morning," recalls Duffy, who was a lieutenant colonel in the Massachusetts Air National Guard at the time.
Duffy not only witnessed the most horrific day in modern U.S. history - his story is one of the numerous footnotes in The 9/11 Commission Report.
Aided by more than 200,000 FBI interviews, the report is the official accounting of September 11, 2001. It's an exhaustive examination of what happened leading up to and during that day when Muslim extremist hijackers commandeered four planes and flew them into New York's World Trade Center Towers, the Pentagon in Washington, and a field in western Pennsylvania.
CNN spoke to eight of the men listed in the commission report's footnotes - the ticket agents, the pilot on alert to shoot down a passenger jet, the maintenance worker who took a phone call from a flight attendant on one of the ill-fated jets.
Meet the everyday citizens who went to work on September 11, 2001, and unwittingly became a part of history. Watch CNN Presents "Footnotes of 9/11" on Tuesday, September 6 at 11:00 p.m. ET, and again on Sunday, September 11 at 9:00 p.m. ET.FULL STORY