A woman has been arrested in Yemen for allegedly mailing the package bombs meant to target Jewish centers in Chicago -- a scare that prompted searches of cargo flights in Newark, Philly and one of a passenger plane in New York City, security officials in Yemen said.
But U.S. officials caution while she may have helped in the plot, the alleged ringleaders remain on the loose.
"The circle of people who were possibly behind this was small to begin with," said one security official speaking on condition of anonimitiy. "That circle has gotten a lot smaller in the last 24 hours."
Another official said intelligence analysts now think they know who the bomb-maker and mastermind of the bomb plot is but has not yet been tracked. Officials said his name is Ibrahim Al Asiri, a Saudi national who is believed to be a top bomb maker for al Qaeda in Yemen.
These guys are well-educated in what they are doing," said NBC Security Analyst Evan Kohlmann. "They are some of al Qaeda's best."
Yemeni officials said the woman suspect is a medical student and her phone number was on the packing slips.
Sunday, a source in Yemen said security sources in Sanaa believe the investigation has revealed that another woman used the name of Hanan al Samawi when she went to mail the packages.
British officials said the bombs were real. The devices were hidden in printer cartridges packed with about a pound each of the powerful explosive PETN and officials in Britain said they could have taken down an airliner if it exploded on board.
"At this stage we have no information another terrorist attack is imminent," said British Home Secretary Theresa May.
The PETN found in the case is much larger than the amount used by convicted shoe-bomber Richard Reid or the alleged Christmas day bomber who hid explosives in his underwear on a flight to Detroit.
The PETN was hidden in the ink cartrdiges inside computer printers. The white explosive material was connected to wires and cell phone parts. Officials said it is unclear if the triggering device was a timer in the electronics or a phone call to the devices once the packages arrived at the Chicago destinations. Investigators said while the explosives are real, it is still too soon to know if the triggering devices were operational.
Investigators said one theory is the terrorists may have actually been targeting passenger airplane, which some experts say carry roughly half the air cargo coming into the U.S.
All day Friday along the East Coast, there were frantic searches of suspicious packages arriving on cargo and passenger planes. Police and FBI agents were seen at New York, Newark and Philadelphia airports checking packages as a precaution.
On Saturday, investigators said they were hopeful the two devices found in Dubai and Britain were the only explosives sent as part of this cargo airlines plot.
Among the searches Friday was an Emriates flight into JFK that had been escorted by U.S. fighter jets Friday when officials learned a package from Yemen was in the cargo hold. An all clear was later given.
UPS cargo planes in Newark and Philadelphia were also searched but no bombs were found. Other flights into JFK that had been carrying mail that had originated in Yemen - including a British Airways flight - were also checked as precaution.
Yemen is increasingly a hotspot for al Qaeda terror plots. Officials said they are taking a look at radical cleric Anwar al Awlaki and al Qaeda-linked bomb makers he is associated with as being behind this plot.
Saudi intelligence officials are being credited with providing the key tip that led officials to track down the two devices. Officials said the information was so good that they even had the specific tracking numbers on the packages.
Officials in Yemen said they are looking into whether any workers at the shipping facilities in that country assisted in the plot. Yemeni government officials have pledged support to track down suspects but many parts of the country are lawless with areas controlled by family groups aligned with extremists.
More than a dozen packages were checked on flights to the U.S. over the last 24 hours. Investigators said as a precaution, they continue to try to track any packages sent from Yemen in recent weeks. Intelligence officials said they have no information that more bombs are out there but they caution the investigation remains fluid.
"Let's hope that intelligence has the complete picture and maybe it is," said Kohlmann. "But until we see Monday or Tuesday pass without anything happening - we need to reserve our confidence until later."
At New York area airports, extra security appeared to be in place. At Kennedy airports, some international passengers arriving from overseas said their luggage was hand searched in addition to going through screening machines.
Security sources also say that Al Samawi was released with the agreement that her father will bring her in if she is wanted for further questioning. They say that Al Samawi was only held in police custody for questionng but did not under the judiciary. There are no official charges against her. She was only brought in for questioning.