Every time there is an anniversary or every time he sees video of that attack, Frost says the images haunt him.
"One of the worst ones that I can't get out of my mind is the exact moment that her plane hit the building. I saw it live. I watched my daughter die live," he said. "That's an image that is burned into my head and it's so hard to get out."
Tom keeps his daughter's room at his Rancho Santa Margarita home as a tribute to her life. There are items from her childhood, as well as the credit card that was found in the debris.
"I miss her more today than I did yesterday and I'll miss her more tomorrow than I did today," Frost said.
He keeps her spirit alive by doing what she would have done: helping others. She keeps him strong through all the memories.
Frost is a long distance runner who has taken part in several marathons all over the country. He says this is the longest and hardest journey he will ever make.
"It's tough to keep going through it," he said. "I had a guy that was one week into 9/11 that told me his daughter got killed with a drunk driving accident. He says it was in all the papers, but 'I'll never have to see it again. You're going to have to live with this, Tom, for the rest of your life. It's never going to go away.' And it hasn't."