President Obama promised today that the country would "not rest until" the people behind the the plot to blow up a Northwest Airlines flight on Christmas Day were caught and brought to justice.
"We will not rest until we find all who were involved and hold them accountable," Obama, who is vacationing in Hawaii with his family, said. "This was a serious reminder of the dangers that we face and the nature of those who threaten our homeland."
"We will continue to do everything that we can to keep America safe in the new year and beyond," the president added.
Umar Farouk Abdulmutallab -- a Nigerian national who had been on the U.S. government's terrorist watch list but not on its no-fly list --- was arrested Christmas Day after authorities say he tried to ignite explosives he carried in his underwear in an attempt to destroy the Detroit-bound passenger aircraft.
Shortly before Obama vowed to go after the perpetrators of the attempt, an al Qaeda group claimed responsibility for the botched bombing.
A husband and wife who were on the flight said they saw Abdulmutallab with a wealthy looking man at the check-in gate, and said it appeared the older man was trying to help him get past security.
Kurt Haskell, a Michigan attorney who spoke with ABC News this afternoon, said the two seemed to be an incongruous pair, because Abdulmutallab looked to him like a poor teenager, not someone the other man, who he described as "Indian, but to me Indian may be Pakistani or Bangladesh or something similar," would likely be with.
FBI officials in Detroit have not commented on the couple's claim.
The president's remarks today came shortly after al Qaeda in the Arabian Peninsula claimed responsibility for the attack, a message that has led the FBI, CIA and the entire U.S. intelligence community to begin an intensive scrub down and go back and look at all the Yemen-related threat intel to see if they have missed anything, or dismissed anything that they should not have.
The agencies launched the internal review almost immediately after the failed attempt and today, sources tell ABC News, a statement from al Qaeda on the Arabian Peninsula telling Americans that "we will strike you with what you have no previous knowledge of, for as you kill you shall be killed, our vengeance is near," is creating more concern.
Senior officials tell ABC News that this threat released today is receiving intense scrutiny from all agencies and the White House. Officials are trying to figure out how to respond.
"This is a dangerous group and we need to take them seriously. They were not specific about their plans, but that clearly was intentional, so as not to tip their hand," one intelligence source told ABC News. This could be a scare tactic or propaganda, the official said. but he added many do not feel the group is making an "idle threat."
The group is based in Saudi Arabia and Yemen and said the attempted Christmas day bombing was in retaliation a Dec. 17 U.S. bombing of their training sites in Yemen.
However, a senior administration official rejected the group's claim about retaliation, pointing out that the bomber, a 23-year-old Nigerian named Umar Farouk Abdulmutallab, was in the field long before that airstrike.
"He had been deployed before Dec. 17," the official told ABC News' Jake Tapper. "They'd like to make this seem like retaliation, but the reason they tried to blow up the plane is because they have a hateful, murderous agenda. And that's why we're on the forward lean against them."
In a statement posted on the internet, the al Qaeda group said it gave explosives to terror suspect Abdulmutallab.
"He managed to penetrate all devices and modern advanced technology and security checkpoints in international airports bravely without fear of death," the group said in the statement.
The device, however, failed to detonate and instead set Abdulmutallab on fire.
The government of Yemen issued a statement today confirming that Abdulmutallab was in Yemen from early August to early December 2009 to study Arabic at a language institute, and that his passport had a valid U.S. visa.
The statement also said investigations are being conducted by Yemeni security agencies to identify any other individuals who may be linked to him, and immediate action would be taken against any accomplices determined.
The government statement said Yemen condemns "such criminal acts that kill innocent civilians" and that it "is and remains an active partner of the international community in the war against terrorism. Efforts of Yemeni security agencies to continue ongoing operations and prosecutions against terrorist operatives from Al-Qaeda will not falter."
White House officials say the president has been briefed regularly and has held secured conference calls with administration officials. But he has no plans to change his travel schedule, a move that has drawn criticism from some Republicans who say the Obama administration hasn't done enough to prevent such terror attacks.
Obama today commended passengers for their "quick and heroic actions," and said he has announced additional security measures on flights, such as adding air marshals. The president has also ordered a review of the incident and of the U.S. "watch list system and how it can be strengthened."
Just a day after she told ABC News the "system has worked really very, very smoothly over the course of the past several days," Department of Homeland Security Secretary Janet Napolitano flip-flopped and admitted that changes need to be made to the passenger screening system.
"Clearly, there's some work that needs to be done to link up what we call the tie, the generic base in which his name had been entered, to those who already have visas," Napolitano said on "Good Morning America" today. "We want to go backward now and review our list processes. ... They clearly need to be adjusted. We need to look at this individual specially, and the screening technology that was deployed."
Obama today said he has directed his national security team to "keep up pressure on those who would attack the country."
Heightened Security in the Wake of Christmas Day Incident
U.S. security agencies are scrambling to determine what went wrong in the screening process.
Abdulmutallab was on the U.S. government's terrorist watch list but not on its no-fly list, which would have prevented him from boarding Northwest Flight 253 from Amsterdam to Detroit.
He was also placed on the United Kingdom's watch list after he was refused a student visa 14 months ago.
British Home Secretary Alan Johnson said today he did not believe Abdulmutallab had been acting alone, and that police and security services in Britain were examining whether he was radicalized while studying at University College London between 2005 and 2008.
The incident was a signal that the U.S. government needs to review the process by which individuals such as Abdulmutallab, are placed on security lists, Napolitano said.
"One of the things that we are doing is going backward. What were the facts that led up to this event, how did this individual get on the plane, why wasn't he flagged at a higher screening level, how did he get an explosive substance onto the plane," Napolitano said on "GMA" today.
In May 2009, a report by the Justice Department Inspector General found problems with how the FBI was managing the terrorism watch list, noting, "We found that the FBI failed to nominate many subjects in the terrorism investigations that we sampled, did not nominate many others in a timely fashion and did not update or remove watch list records as required. Specifically, in 32 of the 216 (15 percent) terrorism investigations we reviewed, 35 subjects of these investigations were not nominated to the consolidated terrorist watch list, contrary to FBI policy."
The Bomber's Family Had Warned the U.S.
Napolitano's remarks on Sunday to CNN brought a sharp rebuke from Rep. Peter King of New York, the top Republican on the Homeland Security Committee.
"It's not reassuring when the secretary of Homeland Security says the system worked," King said. "It failed in every respect."
The Senate Security and Governmental Affairs Committee will hold a hearing next month to examine U.S. security measures.
"We were very lucky this time, but we may not be so lucky next time, which is why our defenses must be strengthened," committee chairman Sen. Joe Lieberman, I-Conn., said in a written statement. "What we know about the Abdulmutallab case raises two big, urgent questions that we are holding this hearing to answer: Why aren't airline passengers flying into the U.S. checked against the broadest terrorist database and why isn't whole body scanning technology that can detect explosives in wider use?"
Abdulmutallab's family had warned U.S. authorities of the increased radicalization of their son, a student at a London university until 2008. His father went to the U.S. Embassy in the capital city of Abuja Nov. 19 to report that he believed his son was being radicalized in Yemen, according to a senior State Department official.
On Nov. 20, the embassy sent out a cable to U.S. embassies worldwide and to the U.S. counterterrorism community alerting them to the information that was provided by Abdulmutallab's father. An intelligence source told ABC News the cable from the State Department noted that the father expressed concern about his son's association with extremists.
There are hundreds of walk-ins to embassies reporting various threats. The State Department's cable triggered the entry into a database run and maintained by the National Counterterrorism Center, but no further threat information was entered because the State Department cable did not contain any specific information about who the son was associated with and the threat they posed.
One senior State Department official did not dispute the possibility -- but could not confirm -- that the State Department may not have realized in November that the individual already held a U.S. visa but noted that someone else in the government, such as security or counterterrorism agencies, would also have had access to that information.
State Department spokesman Ian Kelley said that despite the information provided by the suspect's father, the counterterrorism community determined there was "insufficient" evidence to warrant pulling his U.S. visa. This was not Abdulmutallab's first U.S. visa and he had traveled to the United States under a previous visa.
Abdulmutallab has warned that there are more men like him but U.S. officials have no evidence that the incident was one in a wave of planned attacks. Officials will take Abdulmutallab's DNA sample later today, a fairly routine procedure in a case like this.
A hearing was scheduled for Abdulmutallab today, but a spokesperson for federal prosecutors said it was canceled. There will be a preliminary hearing Jan. 8.
What Happened on Flight 253 Christmas Day?
Abdulmutallab's mission was already in full effect the moment he boarded the plane in Amsterdam, according to ABC News sources.
He had a visa to enter the United States despite his being on the terror watch list. And he paid $3,000 in cash to purchase his ticket, checking no luggage.
Once on the plane, Abdulmutallab walked to seat 19A, next to the wing, and above the fuel tank, apparently choosing the location to maximize the chances of bringing the plane down.
He wanted to blow up the plane over the airport so investigators would find evidence that it was terrorism, the sources said. He went into action just before landing, going to the bathroom and staying there for 20 minutes.
He came back to his seat complaining of a stomachache and covered himself with a blanket. Soon, passengers started noticing fire emitting from his pants.
"There was a bang," passenger Elias Fawaz recalled. "Sounded at first like a balloon went off."
As Abdulmutallab was trying to detonate the bomb in his lap, the wall of the plane caught fire, passengers said.
"I'm sitting here, the flames were leaping up at least this high," said Daniel Huisinga, putting his hands above his head.
The Nigerian national had packed 80 grams of the explosive pentaerythritol tetranitrate, or PETN, the same kind that shoe-bomber Richard Reid used, but even more powerful. But the explosives sewn into Abdulmutallab's underwear failed to ignite, and passengers subdued Abdulmutallab.
One passenger recalled the flight attendant's emotional announcement when the nightmare was over.
"He was just shaking and crying in the speaker, saying, 'The situation is taken care of, the fire is out,'" passenger Richelle Keepman said.
Napolitano said the administration is beginning to deploy new technology at airports.
"There will be lessons learned that we deal with and fix. And that process is ongoing, and as you might imagine, it's ongoing at lightning speed," she said on "GMA." "We are going to get to the bottom of this."
Some experts said while the United States already has new technology to combat this issue, it's not available nationwide, and it's very expensive and considered by some to be intrusive.
"Fewer than 5 percent of the screening posts at airports have the technology necessary to find this sort of thing. The technology exists, but it costs a lot of money, and it's very intrusive and some people think that it invades their privacy," ABC News consultant and former counterterrorism official Richard Clarke said on "GMA." "If we had this expensive, intrusive equipment at all screening posts, we might have been able to stop this."
Umar Farouk Abdulmutallab Increasingly Radicalized
Abdulmutallab's family had warned U.S. authorities of the increased radicalization of their son, a student at a London university until 2008. His father, a former Nigerian banker, had become concerned about his son's disappearance and lack of communication while studying abroad. He first contacted Nigerian security agencies about two months ago, and then some foreign security agencies about a month and a half ago, to seek assistance in finding and returning him home.
"It was while we were waiting for the outcome of their investigation that we arose to the shocking news of that day," the family said in a statement. "The disappearance and cessation of communication which got his mother and father concerned to report to the security agencies are completely out of character and a very recent development, as before then, from very early childhood, Farouk, to the best of parental monitoring, had never shown any attitude, conduct or association that would give concern. As soon as concern arose, very recently, his parents reported it and sought help."
Experts say men such as Abdulmutallab, who live seemingly normal lives, are hard to identify and target.
"This is the truly disturbing part," Clarke said. "They are normal one day and then after a few weeks of watching the Internet and watching al Qaeda videotapes on the Internet, they become radicalized. They reach out in the real world for al Qaeda connections. They get trained.
"It's very hard to see these self-initiating terrorists become terrorists, very hard for U.S. intelligence to pick them up," Clarke added.
The United States needs to move quickly on identifying to whom Abdulmutallab was connected, and address the flaws in the security system that caused this to happen, experts said.
"It's clearly a wake-up call, and it's just like any other crime or criminal behavior. People are always trying to figure out ways around the system and al Qaeda or terrorists or people who want to blow things up are no different," Former FBI agent Brad Garrett told ABC News. "But, the key is: You want to sort that out as quickly as you can because if he is connected to someone else, what other bad acts might be out there waiting to happen?"
Clarke said the Obama administration needs to work more closely with the government of Yemen, which some say has emerged as the new front in terrorism.
"I think we do two things. Long term we work with our Arab friends in the area to address their economic problems and their political instability problems," Clarke said. "Short term, we work with CIA and Defense Department assets and the government of Yemen to go in and find these al Qaeda cells.
"And the untold story here is that the Obama administration is ahead of the curve. The Obama administration has been in Yemen working top CIA officials, top White House officials for over nine months now, working there trying to find these al Qaeda cells and they've done a good job of finding them and attacking them," Clarke said.
The Christmas Day terror attempt has sparked fears of additional bombers in the sky, and an incident Sunday was an indication that even a small matter can unleash a huge government response.
On the same Detroit-bound route two days later, a passenger who spent too much time in the bathroom after getting sick caused a full-scale security alert. Every inch of the plane was searched but the real issue turned out to be food poisoning.
As travelers head back home after the holidays in what is expected to be one of the busiest travel days this year, passengers can expect to see additional security measures and long lines, possibly even causing delays.
ABC News' Kirit Radia and Jason Ryan contributed to this report.