Search for Jet Compounds the Mystery

More than 48 hours after Malaysia Airlines Flight MH370 vanished; the mysteries over its fate have only multiplied.

The Beijing-bound plane made no distress call, officials said, and the Malaysian authorities suggested it might have even begun to turn back to Kuala Lumpur midflight before it disappeared. Despite an intensive international search in the waters along its scheduled route, there were no confirmed sightings of the plane’s wreckage. And electronic booking records showed that the two passengers who were traveling on stolen passports bought their tickets from the same Thai travel agency.

A distraught couple at the Beijing Capital International Airport wait for news about the missing Malaysia Airlines flight.

A distraught couple at the Beijing Capital International Airport wait for news about the missing Malaysia Airlines flight.

The seeming security lapse, which Interpol publicly criticized, might have had nothing to do with what happened to the jet and its 239 passengers and crew. Investigators said they were ruling nothing out, including a catastrophic mechanical failure, pilot error, or both.

With Malaysian officials refusing to release many details of their investigation and sometimes presenting conflicting information, the families and friends of victims became increasingly frustrated.

One woman in Beijing collapsed in tears Sunday night in the hotel ballroom where passengers’ relatives were waiting for news. “Why won’t anyone tell us anything?” she wailed.

The many unknowns also frustrated international security experts attempting to determine whether security breaches might have led to tragedy.

Ronald K. Noble, the secretary general of the International Criminal Police Organization, or Interpol, said, “It is clearly of great concern that any passenger was able to board an international flight using a stolen passport listed in Interpol’s databases.”

“This is a situation we had hoped never to see,” he said, adding that too few countries systematically screen travelers with Interpol’s Stolen and Lost Travel Documents database set up after the terrorist attacks on Sept. 11, 2001. “For years, Interpol has asked, ‘Why should countries wait for a tragedy to put prudent security measures in place at borders and boarding gates?’ ”

A senior American law enforcement official, who has received classified briefings on the global investigation, said that the authorities had not ruled out terrorism in the plane’s disappearance, but that there had been no public claims of responsibility or electronic intercepts of extremists discussing details of any bombing or attack.

“We’re not seeing or hearing anyone claiming anything about this,” the official said.

By early Monday, the search effort had yet to confirm where the plane might have gone down, even as military aircraft and a flotilla of ships from a half-dozen nations, including China, Malaysia, Vietnam and the United States, searched the waters south of Vietnam.

On Sunday, Vietnamese media reported that rescuers had found a yellow object they thought might be part of the aircraft. But the news media later said it turned out to be a coral reef.

Azharuddin Abdul Rahman, the Malaysian civil aviation chief, said samples from an oil slick discovered in the waters had been collected and were being tested to determine if they had come from the plane.

Family members of Firman Chandra Siregar, an Indonesian passenger of flight MH370, watched television at their home in Medan, Indonesia, on Sunday.

Family members of Firman Chandra Siregar, an Indonesian passenger of flight MH370, watched television at their home in Medan, Indonesia, on Sunday.

The flight left the international airport in Sepang, outside Kuala Lumpur, at 12:41 a.m. on Saturday and vanished less than an hour later as it appeared to be cruising at 35,000 feet in calm weather. More details emerged Sunday about the two passengers listed on the manifest using names from an Austrian and an Italian passport reported stolen in Thailand, one in 2012 and the other in 2013. According to electronic booking records, each man bought a one-way ticket on Thursday from a travel agency in a shopping mall in the Thai beach resort of Pattaya. A woman who answered the phone at the agency said she was too busy to talk.

Both men were scheduled to pass through Beijing and continue to Amsterdam before traveling to different cities, Frankfurt and Copenhagen, according to the records.

The senior American law enforcement official confirmed Sunday that Thai officials were investigating a “passport ring” operating on the resort island of Phuket, where both passports were stolen.

Although the official said identifying the two passengers is a top priority for investigators, he noted that false documents were also routinely used in the region by drug smugglers.

Security experts in Asia differed on the significance of the two stolen passports.

Xu Ke, a lecturer at the Zhejiang Police College in eastern China who studies aviation safety and hijackings, said the two men might have been illegal migrants. “There are many cases of falsified and counterfeit passports and visas for illegal migration that our public security comes across, even several cases every day,” he said.

But Steve Vickers, the chief executive of a Hong Kong-based security consulting company that specializes in risk mitigation and corporate intelligence in Asia, said the presence of at least two travelers with stolen passports aboard a single jet was rare.

“It is fairly unusual to have more than one person flying on a flight with a stolen passport,” said Mr. Vickers, who publicly warned a month ago that stolen airport passes and other identity documents in Asia merited a crackdown. “The future of this investigation lies in who really checked in.”

Mr. Azharuddin said investigators were reviewing video footage of the passengers in question. Malaysian officials also said five ticketed passengers failed to board the flight but said that their luggage was removed from the plane before it took off.

Vahid Motevalli, an aviation expert at Tennessee Tech University, in Cookeville, said that since the bombing of Pan Am Flight 103 over Lockerbie, Scotland, in 1988, verifying the identity of passengers had become fundamental.

The Interpol database of stolen passports is considered crucial because it would otherwise be difficult for airline agents to spot well-altered passports.

As they tried to deflect questions about seemingly lax security, Malaysian officials emphasized that their priority was locating the aircraft. They said they had reviewed military radar records and raised the possibility that the aircraft had tried to turn back just before contact with ground controllers was lost.

Gen. Rodzali Daud, the commander of the Royal Malaysian Air Force, said that the authorities were “baffled” by the lack of any distress signals from the aircraft and that a closer look at military radar might have indicated a deviation from the flight path.

But Mikael Robertsson, the co-chairman of Flightradar24, a Stockholm-based service that tracks the majority of the world’s passenger jets, said data gathered by separate civilian receivers in the region did not appear to show the jet turning around.

For now, such conflicting reports seemed to increase tensions.

Prime Minister Najib Razak of Malaysia was quoted saying in the newspaper The Star, that Malaysia would “review all security protocols and, if needed, we will enhance them.”

But Wang Yi, China’s foreign minister, appeared to flash impatience Sunday in a a phone call reported on the ministry’s website.

“The Malaysia Airlines flight has been missing for close to 40 hours,” he was quoted as telling his Malaysian counterpart. “The Chinese government is treating this very seriously.” He asked that Malaysia “constantly” provide updates on the situation.

As of Monday morning, Malaysia Airlines had not eliminated MH370 from its list of regularly scheduled flight numbers. The airline is still selling tickets on its website for a flight with the same number to Beijing on Wednesday morning, departure 12:35 a.m., scheduled arrival 6:30 a.m.