Ron DiFrancesco, his wife Mary and their children Julia and Toby.

Ron DiFrancesco's voice softens and trails off. He barely finishes his sentences as he recalls his experience on Sept. 11, 2001. He speaks as if it happened yesterday.

"It was a living hell," he says. "I was mere seconds from death. ... I didn't know I was going to get out."

DiFrancesco is believed to be the last person out of the South Tower of the World Trade Center before it collapsed. According to some reports, he was one of only four people to escape from above the 81st floor.

A decade later, survivor's guilt still weighs heavily on him.

"I will carry with me to my grave whether I should have taken somebody with me," he says, "I still harbor a lot of guilt.

"Time does heal a bit, but it doesn't make you forget what happened. And I think, for our generation, it's our marking point in history. It changed the world that day," he says.