The full force of the U.S. is now targeted on Ibrahim al-Asiri, the young Saudi bombmaker believed to be behind the two bombs found Friday in UPS and FedEx packages bound from Yemen to Chicago.
Asiri, 28, also said to have been behind last year's attempted Christmas bombing of Northwest flight 253, continues to outmatch billions of dollars in airport security equipment and presents a clear and present danger.
"We need to find him," said John Brennan, President Obama's top antiterrorism advisor.
American officials now concede that Asiri's two latest bombs would have made it onto flights to the U.S. but for the Saudi intelligence service providing the parcel tracking numbers.
Said Homeland Security Secretary Janet Napolitano, "We were able to identify by where they were emanating from and package number, where they were located."
The bombs were cleverly disguised inside Hewlett-Packard printers being shipped along with clothes, books and a tourist souvenir.
Asiri packed the toner cartridge with explosives and added the circuit board of a cell phone--something that did not stand out in state of the art cargo screening.
"We're dealing with an ever changing, ever-evolving threat," said Napolitano.
While the packages were addressed to two synagogues in Chicago, US officials now agree with an initial British estimate that the UPS and FedEx cargo planes that were to carry the parcels over the Atlantic were the real targets of the plot.
"At this point," said Brennan, "we, I think, would agree with the British that it looks as though they were designed to be detonated in flight."
The cell phone trigger would have made it possible to detonate the cargo bombs as the planes approached or flew over an American city.
"It would cause catastrophic damage, it would send debris all over the cities" said Kevin Barry, a former NYPD bomb squad detective now with the International Association of Bomb Technicians and Investigators. "There's also a flight crew on that plane too."
Authorities in Yemen have released on bail a 22-year-old female engineering student whose name and phone number were on the shipping documents for the two bombs sent to the United States.
A lawyer for Hanan Samawi told ABCNews.com that the young woman had returned home after being held and questioned.
The lawyer said Samawi's father had been instructed to have his daughter avoid news reporters.
A Yemeni official briefed on the investigation said the suspect "is not allowed to leave the country pending further questioning."
The official said the shipping agent who received the packages was called in to identify her and said Samawi "was not the person who signed the shipping manifesto."
The official said authorities now believe it is a case of "stolen identity by an individual who knew the detained suspect's full name, address and telephone number."
Her arrest had been trumpeted by the President of Yemen, Ali Abdullah Saleh, as evidence of its cooperation with the U.S. and others to combat terrorism.
But as her fellow students mounted a protest Sunday at a university, her lawyers questioned why anyone involved in the plot would use their real name and phone number to ship a bomb.
John Brennan went on ABC News Sunday to warn that authorities are hunting for other packages like the ones containing powerful explosives that were found Friday on UPS and FedEx cargo jets bound for the United States.
"We can't presume that there are none others that are out there," John O. Brennan told ABC News This Week host Christiane Amanpour. "What we're trying to do right now is to work very closely with our partners overseas to identify all packages that left Yemen recently and to see whether or not there are any other suspicious packages out there."
Brennan said the U.S. was "very fortunate" to have received help from Saudi Arabia, and that the assistance "saved lives here."
"Once they received the information, they contacted us immediately, and it was a race against the clock to find those packages, to neutralize them," he said. "And so we owe a debt of gratitude to the Saudis. I think their actions really saved lives here."
The administration's decision to publicly identify the Saudis as the source of that critical tip has brought some criticism, though, from Republicans on Capitol Hill. The ranking Republican on the Senate Intelligence Committee told ABC News Sunday that the White House was "stupid" to identify Saudi Arabia as the source of the tip that helped foil the Yemen-based terror plot to sent bombs to the United States by UPS and FedEx.
"Why do you finger the Saudis?" Sen. Kit Bond of Missouri said Sunday. "When you identify your sources, you may make it easier for Al Qaeda to retaliate. And you may embarrass the Saudis."
Bond said he and others in Congress have more questions about the way American intelligence responded to the potentially deadly terror plot that was foiled Friday. Chief among them is to determine when, exactly, the intelligence community received the detailed tip that enabled them to identify and remove the packages from two cargo jets.
It is a concern, Bond said, that the bombs appear to have traveled aboard at least one passenger flight, and that both packages were able to be loaded on cargo planes without detection.
Bond said the only possible reason he could imagine for the Saudis wanting to be fingered as the source of the intelligence would be if they wanted to build good will on Capitol Hill.
"If any of my colleagues have doubt that they can be friendly, I suppose this would send a strong signal that they can be friendly," Bond said.
White House officials told ABC News that the decision to identified the Saudis was "coordinated every step of the way with the Saudis, and that they were aware that they'd be named before we did it."