Mary Fetchet's mission began on the morning of Sept. 11, 2001, when her 24-year-old son, Brad -- an equity trader -- was killed in the attacks on the World Trade Center. She has since devoted her life to making America safer.
"We need to know systematically the truth about what these failures were, government failures across the board that made us so vulnerable," she said.
Fetchet, a social worker from Connecticut, banded together with others who lost loved ones in the days after the attacks. They began lobbying for an official investigation of the 9/11 attacks, something President Bush at first resisted.
"I'm not intimidated by anyone," Fetchet said. "I can't live with the fact that people in charge are telling me, assuring me, that this is going to happen again."
Their work paid off. The president changed course and an independent commission was established to investigate the intelligence failures that led to the attacks.
During the commission's highly publicized hearings, some of the nation's top intelligence officials testified to failures in America's defenses and missed opportunities to stop the attacks. Fetchet and the others sat in the back of the room, hanging on every word.
She listened as former counterterrorism czar Richard Clarke apologized for the government's shortcomings: "Those entrusted with protecting you failed you, and I failed you," he said. "And for that failure, I would ask, once all the facts are out, for your understanding and for your forgiveness."
Said Fetchet: "That was the first time, certainly, that we've heard anyone apologize."
After the commission issued its recommendations on how to make America safer, it was Fetchet and her group who demanded action from Congress and Bush.
Sen. Joseph Lieberman, D-Conn., helped write legislation based on the recommendations.
"Mary Fetchet and the other survivors of September 11th just got involved -- a small group of committed people -- and they changed the world," he said.
Earlier this month -- thanks, in part, to Fetchet's efforts -- Congress passed and the president signed into law sweeping changes affecting the nation's intelligence-gathering agencies.
"It is our moral obligation to be sure that our government is doing everything they can to make sure this is a safer country," Fetchet said, "so that no one is walking in my shoes."
ABC News' Elizabeth Vargas filed this report for "World News Tonight."