Others, though, had no reason for hope and were left to sift through memories or consider the painful ironies that brought their loved ones into doomed planes and buildings.
Many World Trade Center workers phoned their families to report the first strike had missed them, only to vanish in the second.
Businesses, too, searched for their missing, with phone trees and e-mails delivering mixed news. Morgan Stanley, for instance, had 40 of its 3,700 trade center workers unaccounted for Thursday. MMC, an insurance agency, knew the whereabouts of just 1,000 of its 1,700 employees who might have been there.
Among the missing Thursday were a growing number with ties to Chicago and the rest of Illinois.
John P. O'Neill
John P. O'Neill was one of America's best minds in its fight against terrorism. For the last several years, the 31-year FBI veteran had trained his expertise on Osama bin Laden, a prime suspect in Tuesday's attacks.
But O'Neill, 50, retired two weeks ago from the FBI after becoming the subject of a bureau investigation because he misplaced a briefcase--later recovered-- containing highly classified information. Authorities said last month that the briefcase included a report outlining virtually every national security operation in New York.
While serving as assistant special-agent-in-charge of foreign counter-intelligence and terrorism in the FBI's Chicago field office in the early 1990s, he worked on the probe of the 1993 bombing of the World Trade Center.
He then became counterterrorism chief in the bureau's New York office, where he led investigations of several terror strikes attributed to the Saudi extremist, including the attacks on the USS Cole in Yemen last year and the U.S. embassies in Nairobi and Tanzania in 1998.
"He was so dedicated to wiping him out. He was obsessed with getting him," said Valerie James, his longtime companion.
After leaving the bureau, O'Neill became director of security for the World Trade Center, where he was working Tuesday morning.
He called James from outside the trade center shortly after the hijacked planes struck the twin towers. "He said, `I'm OK, I love you. There's body parts everywhere. I've got to go because I have to evacuate the building,' " said Stacy James of Oak Park, Valerie James' daughter.
"I keep telling my mom that he's in a hospital somewhere," Jerome James said. "But he was very serious about his job, and that's the part that scares me the most; he probably did go and help people."
Cmdr. Dan Shanower, 40, a U.S. Navy intelligence officer who grew up in Naperville, was believed to be among those working at the Pentagon when a plane struck.
Shanower's family has lived in Naperville for years, and Dan Shanower's father, Don, is a former North Central College professor, family friend Dick Eastman said.
A Naperville Central High School graduate, Shanower served "all over the globe," said Eastman. He also wrote essays for the U.S. Naval Institute magazine Proceedings, including one in 1997, called "Freedom Isn't Free."