GWEN IFILL: The U.S. government launched a top-to-bottom search for answers after a would-be bomber tried to destroy a U.S. airliner on Christmas Day. But every day has brought new questions, and, today, a claim of responsibility.
The president interrupted a Christmas holiday vacation in Hawaii to offer his first public remarks on the attempts to bring Northwest Airlines Flight 253 down.
U.S. PRESIDENT BARACK OBAMA: And a full investigation has been launched into this attempted act of terrorism, and we will not rest until we find all who were involved and hold them accountable.
GWEN IFILL: Mr. Obama confirmed the government is reviewing screening procedures, as well as its watch list system of known and suspected terrorists.
Shortly before he spoke, the group al-Qaida in the Arabian Peninsula claimed responsibility for the attempt, saying in an Internet posting that it came in response to U.S. strikes at its members in Yemen.
In his remarks today, President Obama vowed to continue hunting al-Qaida.
BARACK OBAMA: The United States will more do more than simply strengthen our defenses. We will continue to use every element of our national power to disrupt, to dismantle and defeat the violent extremists who threaten us, whether they are from Afghanistan or Pakistan, Yemen or Somalia, or anywhere where they are plotting attacks against the U.S. homeland.
GWEN IFILL: What's known so far?
Twenty-three-year-old Umar Farouk Abdulmutallab bought his ticket with $2,800 in cash on December 16. He checked no bags. He boarded the plane in Lagos and cleared security there, as well as in Amsterdam, where the flight made a stopover.
The jet was on final approach to Detroit when Abdulmutallab allegedly tried to ignite explosives concealed under his clothing. Authorities said he used a syringe to inject triggering chemicals into a small bag of crystalline explosive known as PETN.
Instead of blowing up, the bag simply caught fire. Then passengers and crew subdued the suspect. Abdulmutallab was treated for burns and sent to a low-security federal prison in Milan, Michigan, about 45 miles south of Detroit.
On Sunday, Homeland Security Secretary Janet Napolitano defended the government's handling of the case.
JANET NAPOLITANO, U.S. Homeland Security Secretary: The system worked. Everybody played an important role here. The passengers and crew of the flight took appropriate action. Within literally an hour to 90 minutes of the incident occurring, all 128 flights in the air had been notified to take some special measures, in light of what had occurred on the Northwest Airlines flight.
GWEN IFILL: But, by this morning, Napolitano did concede the system failure.
JANET NAPOLITANO: I don't any think secretary of homeland security would sit before you and say she was happy that someone got aboard a U.S.-bound air carrier, as this individual did, carrying the material that this individual was carrying. So, we have a lot of work to do.
GWEN IFILL: That statement came in the wake of reports that Abdulmutallab had been barred from reentering Britain and that he wasn't on a similar list here.
His family in Nigeria said today the man's father, a prominent banker, had warned U.S. authorities in October about his son's increasingly extremist views. Almost immediately after the Detroit incident, authorities in the U.S. and abroad stepped up security during the busy holiday travel season.
JESSALYN SHAMESS: It's definitely a little bit more stressful flying today than -- than I thought it was going to be.
GWEN IFILL: In the U.S., the Transportation Security Administration began requiring passengers on flights from overseas to be screened a second time at the gate.
TRAVELER: You know, probably, though, it's like, you know, we would rather be safe than sorry any time, yes.
TRAVELER: And if you have got nothing to hide, well, you shouldn't have any problem with it.
TRAVELER: Problems, yes.
GWEN IFILL: And during the final hour of some flights, passengers were instructed to stay seated with no personal items on their lap.
JENNIE LLOYD: When we were on the plane, we couldn't have blankets or pillows in our laps.
GWEN IFILL: For domestic travelers, random security checks have been increased and air marshals added.
ELAINE VONG: Every single item was examined. They took it out and they used their sniffer test or whatever. They were running it along inside. They wanted everything out of the bag and examine the interior of the bag.
GWEN IFILL: But, by today, some of those procedures were already being eased a bit.
This was the sixth terror incident aboard a commercial flight in the U.S. in 10 years, including 9/11. That works out to be about one attack for every 16.5 million flights.
But ABC News reported, Abdulmutallab has told the FBI that other operatives are being trained in Yemen to launch new attacks.