At an undisclosed location in Northern Virginia, unheralded heroes in the war on terrorism sit all day in a windowless room staring at computer screens.
At the secretive National Targeting Center, officers for the Customs and Border Protection agency spend hours trolling through lists and combing databases.
Watch 'World News with Diane Sawyer' for more on our Persons of the Week, tonight on ABC.
Customs officer Daniel Donohue reviews more than 500 names a day.
"It can be tedious, it can be stressful," said Donohue. "But at the same time, there's a lot of teamwork involved."
Tedious, perhaps. But this week, the life and death importance of the work could not be more clear.
When Donohue came to work last Monday night, he heard the name of a person of interest, Faisal Shahzad, who allegedly is behind last weekend's Times Square bomb attempt.
Donohue started his shift, beginning the work of looking through manifests of flights about to take off.
As he looked at the names, suddenly, "that person just happened to hit my screen," Donohue said.
He remembered the name and double-checked it against his list. Realizing that there was no time to lose, he rushed to tell another officer that Shahzad was on a plane bound for Dubai.
"He was like, 'When does the flight leave?'" Donohue recalled. "And I was like, 'In 20 minutes.' ... And then the phones started going, and he notified the watch commander. It went so fast."
The watch commander was Petra Horne. She made the split-second decision to call Kennedy Airport.
"The supervisor I was talking with was literally running down the runway," said Horne.
Minutes later, she got word that Kennedy officials had stopped the flight and captured their man.
"I was able to breathe," said Horne.
For both, it was another day at the office, doing work so secretive that family members know little about it.
"My wife, she was like, 'Did you read the news that they arrested that guy in Times Square?'" said Donohue. "'Yeah, I did.' And she was like, 'Did you have any part in that?' And I was like, 'Well, kind of,'" he said, laughing.
The next day, Donohue was ready to go back to work like a watchman, seated at his post again.
"It was overwhelming," he said, reflecting on the experience. "But it's always something. ... This is what I do, you know. This is my job."