Vietnamese authorities searching waters for the missing Boeing 777 jetliner spotted an object Sunday that they suspected was one of the plane's doors, as international intelligence agencies joined the investigation into two passengers who boarded the aircraft with stolen passports.
More than a day and half after Malaysia Airlines Flight MH370 disappeared with 239 people on board, no confirmed debris from the plane had been found, and the final minutes before it went missing remained a mystery. The plane lost contact with ground controllers somewhere between Malaysia and Vietnam after leaving Kuala Lumpur early Saturday morning en route to Beijing.
Searchers in a low-flying plane spotted what appeared to be a door from the missing jet, the deputy chief of staff of Vietnam's army, Lt. Gen. Vo Van Tuan, was quoted as saying by the state-run Thanh Nien newspaper. It was found in waters about 60 miles (90 kilometers) south of Tho Chu island, in the same area where oil slicks were spotted Saturday.
"From this object, hopefully (we) will find the missing plane," Tuan said. Two ships from the maritime police were heading to the site.
The missing plane apparently fell from the sky at cruising altitude in fine weather, and the pilots were either unable or had no time to send a distress signal - unusual circumstances under which a modern jetliner operated by a professional airline would crash.
Authorities were checking on the identities of two passengers who boarded the plane with stolen passports. On Saturday, the foreign ministries in Italy and Austria said the names of two citizens listed on the flight's manifest matched the names on two passports reported stolen in Thailand.
"I can confirm that we have the visuals of these two people on CCTV," Malaysian Transport Minister Hishammuddin Hussein said at a news conference late Sunday, adding that the footage was being examined. "We have intelligence agencies, both local and international, on board."
"Our focus now is to find the aircraft," he said, adding that finding the plane would make it easier for authorities to investigate any possible foul play.
Interpol confirmed that it knew about the two stolen passports used to board the ill-fated plane, but said no one checked its vast databases on stolen documents.
In a forceful statement, Interpol Secretary General Ronald Noble chided authorities for "waiting for a tragedy to put prudent security measures in place at borders and boarding gates."
"Now, we have a real case where the world is speculating whether the stolen passport holders were terrorists," Noble said. "Interpol is asking why only a handful of countries worldwide are taking care to make sure that persons possessing stolen passports are not boarding international flights."
The thefts of the two passports - one belonging to Austrian Christian Kozel and the other to Luigi Maraldi of Italy - were entered into Interpol's database after they were stolen in Thailand, the police body said. Kozel's passport was stolen in 2012 and Maraldi's last July.
A telephone operator on a China-based KLM hotline confirmed Sunday that passengers named Maraldi and Kozel had been booked to leave Beijing on a KLM flight to Amsterdam on Saturday. Maraldi was to fly on to Copenhagen, Denmark, and Kozel to Frankfurt, Germany.
She said the pair booked the tickets through China Southern Airlines, but she had no information on where they bought them.
Having onward reservations to Europe from Beijing would have meant the men, as holders of EU passports, would not have needed visas for China.
Interpol said it and national investigators were examining other suspect passports and working to determine the true identities of those who used the stolen passports to board the Malaysia Airlines flight.
White House Deputy National Security Adviser Tony Blinken said the U.S. was looking into the stolen passports, but that investigators had reached no conclusions.
In addition to the plane's sudden disappearance, which experts say is consistent with a possible onboard explosion, the stolen passports have strengthened concerns about terrorism as a possible cause. Al-Qaida militants have used similar tactics to try to disguise their identities.
Other possible causes included a catastrophic failure of the plane's engines, extreme turbulence, or pilot error or even suicide. Establishing what happened with any certainty will need data from flight recorders and a detailed examination of any debris, something that will take months if not years.
Malaysia's air force chief, Rodzali Daud, said radar indicated that before it disappeared, the plane may have turned back, but there were no further details on which direction it went or how far it veered off course.
"We are trying to make sense of this," Daud said at a news conference. "The military radar indicated that the aircraft may have made a turn back, and in some parts this was corroborated by civilian radar."
Malaysia Airlines Chief Executive Ahmad Jauhari Yahya said pilots are supposed to inform the airline and traffic control authorities if the plane does a U-turn. "From what we have, there was no such distress signal or distress call per se, so we are equally puzzled," he said.
A total of 34 aircraft and 40 ships were deployed to the area by Malaysia, Thailand, Australia, Singapore, Indonesia, China and the United States, in addition to Vietnam's fleet.
Of the 227 passengers and 12 crew members on board, two-thirds were Chinese, while the rest were from elsewhere in Asia, Europe and North America, including three Americans.
Family members of Philip Wood, an IBM executive who was on board the plane, said they saw him a week ago when he visited them in Texas after relocating to Kuala Lumpur from Beijing, where he had worked for two years.
"There is a shock, a very surreal moment in your life," said Wood's brother, James Wood.
The other two Americans were identified on the passenger manifest as 4-year-old Nicole Meng and 2-year-old Yan Zhang.
After more than 30 hours without contact with the aircraft, Malaysia Airlines told family members they should "prepare themselves for the worst," Hugh Dunleavy, the commercial director for the airline, told reporters.
Finding traces of an aircraft that disappears over sea can take days or longer, even with a sustained search effort. Depending on the circumstances of the crash, wreckage can be scattered over many square kilometers (miles). If the plane enters the water before breaking up, there can be relatively little debris.
A team of American experts was en route to Asia to be ready to assist in the investigation into the crash. The team includes accident investigators from the National Transportation Safety Board, as well as technical experts from the Federal Aviation Administration and Boeing, the safety board said in a statement.
Malaysia Airlines has a good safety record, as does the 777, which had not had a fatal crash in its 19-year history until an Asiana Airlines plane crashed last July in San Francisco, killing three passengers, all Chinese teenagers.