(CNN) -- The explosive found hidden in a package on a plane in the United Arab Emirates on Friday may have traveled on passenger planes to get there, airline officials said Sunday.
The explosive, along with a similar device found in the United Kingdom, appear to have been designed to detonate on their own, without someone having to set them off, the top White House counterterrorism official told CNN.
"It is my understanding that these devices did not need somebody to detonate them," said John Brennan, President Barack Obama's assistant for homeland security and counterterrorism.
U.S. investigators believe al Qaeda bomb maker Ibrahim Hassan al-Asiri, 28, is linked to that package and another one found on a second airplane in Britain's East Midlands Airport on Friday, a federal official, who was briefed by authorities, told CNN Sunday. Both packages were addressed to synagogues in Chicago, Illinois.
Al-Asiri, who is thought to be in Yemen, is a Saudi who was high on Saudi Arabia's list of most wanted published in February 2009. He is also believed to be the bomber who designed last year's failed Christmas Day underwear bomb.
Separately, an engineering student arrested in Yemen was released Sunday, along with her mother, according to her father, Mohammed Al-Samawi. She was earlier identified as Hanan Al-Samawi, a fifth-year student at Sanaa University in the Yemeni capital, said Abdul-Rahman Barman, a human rights attorney and activist who said he was asked to represent her.
A high-level source in the United Arab Emirates said Hanan Al-Samawi's name was found on the cargo manifest of the device found in Dubai.
Also arrested was her mother, Amatilullah Mohammed. Barman had said the mother's arrest was illegal and said holding the two in an undisclosed location was "a criminal act."
Authorities do not have any American suspects at this time, a U.S. official said.
Two schools in Yemen were being looked at in connection with the plot and had been on the radar of U.S. officials before, the official said.
The explosive device found in Dubai, United Arab Emirates, was contained in a Hewlett-Packard printer, and had a motherboard originating from a mobile phone, but did not have a SIM card in it, the high-level source told CNN.
The device was professionally assembled, the source said. The motherboard was connected by a striker to the printer head and then to the cartridge, which was filled with explosives.
Authorities have the serial number of the motherboard and the printer, and are searching to see where it was sold, how it was paid for and what information they can glean about the people who performed those transactions, according to the source.
Authorities believe an explosive device found at the United Kingdom's East Midlands airport flew from Yemen to a Persian Gulf state, then to Cologne, Germany, the official said. The device was then transferred onto a UPS plane.
Investigators are still attempting to retrace the route of the Dubai device, according to the high-level official. Some believe it went to Doha, Qatar, on Qatar Airways, where it spent the night before traveling to Dubai the following day. However, it does appear the devices did fly on commercial passenger planes, the high-level official said.
Screening the devices would have been difficult, since printers normally contain computer parts and wires, according to Richard Quest, CNN's aviation correspondent.
Qatar Airways, which said earlier Sunday that it had flown the device from Yemen to Dubai for FedEx, is no longer certain that is true, a senior airline source said. The airline is investigating the possibility that the explosives flew on another airline after finding inconsistencies in information it was given, the source said.
An airline spokesman said earlier that two Qatar Airways passenger planes had carried the package.
Emirates Airways, which also flies from Yemen to the United Arab Emirates, said as far as it is aware, it had not carried the package.
The package was being sent by FedEx, which uses other airlines to get parcels out of Yemen because it does not fly there itself.
The two devices found Friday look like they were put together by the same bomber who designed last year's failed Christmas Day underwear bomb, a U.S. government official told CNN.
"The thinking is it's the same person or group of people that built the underwear bomb, because of the way it's put together," said the official, who had been briefed by multiple U.S. authorities and law enforcement sources. "But this one is about four times as powerful."
American authorities are now endorsing British Prime Minister David Cameron's position that the explosives were designed to take down an airplane, the official said. However, a U.S. official said Sunday the United States has not drawn any conclusions on the intent of the bombs and whether they were intended to explode in flight, at the synagogues or somewhere else.
American and British authorities think al Qaeda's branch in Yemen is linked to the plot.
A key figure in the group is the American-born Yemeni militant cleric Anwar al-Awlaki, whom U.S. authorities have linked to Fort Hood shooting suspect Maj. Nidal Hasan and the man accused in the Christmas Day bomb attempt.
Brennan on Friday declined to name al-Awlaki specifically as a suspect.
"Anybody who's associated with al Qaeda in the Arabian Peninsula is a subject of concern," he said.
Yemen is investigating the shipping agency that sent the packages, its President Ali Abdullah Saleh said Saturday, based on information provided by the United States and United Kingdom, who in turn are getting tips from Saudi Arabia.
The United Kingdom is sending a security team to help with Yemen's investigation, Saleh said.
A specific explosive was found in both Friday's devices and in the foiled underwear bomb attempt in 2009, a source close to the investigation said.
It's a highly explosive organic compound called PETN, which belongs to the same chemical family as nitroglycerin, the source said. Six grams of PETN are enough to blow a hole in the fuselage of an aircraft.
PETN was allegedly one of the components of the bomb concealed by Umar Farouk AbdulMutallab, the Nigerian man accused of trying to set off a bomb hidden in his underwear aboard a Northwest Airlines flight as it approached Detroit, Michigan, on December 25.
"The quantity of PETN in these [new] devices was about five times the volume used at Christmas" by AbdulMutallab, Col. Richard Kemp, the former chairman of the British government's Cobra Intelligence Group, told CNN affiliate ITN.
Yemen's president said his country is cooperating with the U.S., the U.K., and Saudi Arabia. The U.S. Transportation Security Administration is sending six inspectors to Yemen to help improve cargo security, an official with the agency said Sunday.
"Even before this incident, 100 percent of identified high-risk cargo on inbound passenger planes was being screened," TSA Administrator John S. Pistole said in a statement Sunday, noting that security procedures will evolve based on the latest intelligence information.
Over the past several months, Yemen, which wants to be seen as a committed partner in the fight against terrorism, has launched several offensives against al Qaeda in its country, but has not captured al-Awlaki.
"We acknowledge that we have a problem with terrorism, specifically the presence of al Qaeda, and we continue to pay a high price," Saleh said.
The Yemeni government imposed new security measures at local airports, the SABA news agency said Sunday, including "unusual check methods on outgoing packages from Yemeni airports."
Meanwhile, U.S. authorities were grateful for a tip from Yemen's oil-rich neighbor, Saudi Arabia, alerting them to the suspicious packages. Saudi officials provided tracking numbers of the two packages, enabling quick tracing to the United Kingdom and Dubai, a source told CNN.
CNN's Bharati Naik, Caroline Paterson, Jeanne Meserve, Mohammed Jamjoom, Susan Candiotti and Carol Cratty contributed to this report.