Looking over some names on the monument, Chertoff noticed a college classmate; it was the first time he'd heard that his old acquaintance had been a victim of the worst terrorist attacks in American history.
"Sept. 11 is a defining moment -- not only for our country, but for many of us personally," he said during a mid-September speech in Philadelphia.
In fact, he added: "We are still discovering new things about that day and our response to that day."
The World Affairs Council of Philadelphia organized the program, held at the Union League, that featured Chertoff, who, in February 2005, became the second secretary of homeland security, replacing former Pennsylvania Gov. Tom Ridge.
Born in Elizabeth, N.J., Chertoff grew up the son of a Conservative rabbi. A former federal judge of the 3rd Circuit Court of Appeals, he earlier worked at the Justice Department and helped trace the 9/11 attacks to Al Qaeda.
Terror the Gravest Threat
He said he gave up his lifetime judicial appointment to accept President George W. Bush's offer to head the department because he views the threat posed by terrorism as the great challenge of the generation.
His predecessor is generally regarded to have had only mixed success in taming the large bureaucratic apparatus that falls under the rubric of homeland security. Chertoff himself took some criticism for the federal government's response to Hurricane Katrina. The much-maligned Federal Emergency Management Agency falls under his department.
Chertoff steered clear of that particular topic, and instead laid out what he viewed as some of the biggest gains made in securing the home front. He cited the department's creation of the Domestic Nuclear Detection Office that's working to create a "global nuclear-detection architecture."
He also said the department is trying hard to upgrade its database of fingerprints -- it will begin collecting 10 sets of fingerprints of foreign nationals instead of two to increase accuracy -- and is also improving how Homeland Security can share fingerprint records with the Department of Justice, as well as state and local law enforcement.
Since 2004, foreign nationals have been required to give their prints when arriving at American airports and seaports.
"We have done a lot to protect ourselves against known terrorists," said Chertoff. "But how do we screen against unknown terrorism?"
And that, he stated, is one the biggest issues confronting counterterrorism specialists.
"We want to make sure we don't destroy what we are trying to protect," he added. "We are balanced. We take into account the needs of the economy and civil liberties."
When asked by an audience member whether Philadelphia had been shortchanged as far as homeland-security funding is concerned, he responded that the city has received roughly $100 million from the department since 2002.
"We have to be mature about the fact that it's not possible to eliminate all risk," maintained Chertoff.
"Five years from now, on the 10th anniversary, I hope we'll still be able to say there's only been one attack. We will work tirelessly to achieve that goal."