The mystery of what happened to a Malaysia Airlines flight that disappeared with 239 people on board early Saturday appeared to deepen Sunday when Malaysia's air force chief told reporters that military radar indicated that the plane may have turned from its flight route before losing contact.

Air force chief Rodzali Daud didn't say which direction the plane might have taken when it apparently went off route.

"We are trying to make sense of this," he told a media 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 were supposed to inform the airline and traffic control authorities if the plane does start to return. "From what we have, there was no such distress signal or distress call per se, so we are equally puzzled," he said.
Earlier Sunday, Malaysia's defense and transport minister said that the identities of four of the plane's passengers are being investigated as "suspect." Hishammuddin Hussein, who holds both ministerial positions, said that "the four names are with me," but added that the investigation was focusing on "the entire passenger manifest." Hussein also said that investigators from the FBI had joined the probe.

Scores of ships and aircraft from across Asia resumed searching the South China Sea and the west coast of Malaysia Sunday for any sign of the plane, which was en route to Beijing from Kuala Lumpur. There was still no confirmed sighting of debris in the seas between Malaysia and Vietnam where it vanished from radar screens. The weather was fine and the plane was already at cruising altitude, making its disappearance all the more mysterious.

Just 9 percent of fatal accidents happen when a plane is at cruising altitude, according to a statistical summary of commercial jet accidents done by Boeing. The plane was last inspected 10 days ago and found to be "in proper condition," Ignatius Ong, CEO of Malaysia Airlines subsidiary Firefly airlines, said at a news conference.

U.S. officials said late Saturday that a team of safety experts had been dispatched to Southeast Asia to assist in the investigation. Officials from the National Transportation Safety Board told Fox News that the team, which includes investigators from the agency and technical experts from the Federal Aviation Administration and Boeing, had been sent to the region despite the fact that the plane had not been located due to the lengthy travel time from the U.S. and the team's desire to be in a position to assist local authorities right away.

On Saturday, the investigation into the plane's disappearance took an unusual turn after officials in Italy and Austria revealed that two people aboard the plane were traveling with passports reported stolen in Thailand.
Italy’s Foreign Ministry said that an Italian man, Luigi Maraldi, who was listed on the manifest as a passenger, reported his passport stolen last August.

The Austrian Foreign Ministry also confirmed that a man listed on the official manifest matched an Austrian passport reported stolen two years ago in Thailand, and that the Austrian was not on the plane. The foreign ministry did not release the man's name, but he has since been identified by Sky News as Christan Kozel
A U.S. official told Fox News that a key priority is clarifying the status of the passports, whether they were lost or stolen, and determining through airport security screening and video who exactly got on the flight under those names.

The BBC reported Sunday that the two stolen passports were used to book tickets on the fight to Beijing, as well as on connecting flights from Beijing to destinations in Europe. The purchases reportedly took place almost simultaneously, and the tickets were numbered consecutively.

Meanwhile, a former intelligence official told Fox News that the information about stolen passports from two adjacent European countries, combined with recent warnings for flights to the United States about the risk of possible shoe bomb attacks, is concerning.

The plane was carrying 227 passengers, including two infants and 12 crew members when it “lost all contact,” with Subang Air Traffic Control at 2:40 a.m., two hours into the flight, the airline said. The plane was expected to land in Beijing at 6:30 a.m. Saturday.

The airline said there were 152 passengers from China, 38 from Malaysia, seven from Indonesia, six from Australia, five from India and three from the U.S. and others from Indonesia, France, New Zealand, Canada, Ukraine, Russia, Taiwan and the Netherlands.

The U.S. State Department later confirmed in a statement that three Americans were aboard the jetliner.
In the United States, a friend confirmed to the Associated Press that an IBM executive from North Texas named Philip Wood had been aboard the jet.

Freescale Semiconductor, a company based in Texas, confirmed Saturday that 20 of its employees -- 12 from Malaysia and eight from China -- were passengers.

"At present, we are solely focused on our employees and their families," said Gregg Lowe, president and CEO of the company said in a statement. "Our thoughts and prayers are with those affected by this tragic event."

Vietnamese air force planes spotted two large oil slicks late Saturday in the first sign that the aircraft had crashed. The slicks were each between 6 miles and 9 miles long, the Vietnamese government said in a statement.

There was no confirmation that the slicks were related to the missing plane, but the statement said they were consistent with the kinds that would be produced by the two fuel tanks of a crashed jetliner.

The lack of a radio call "suggests something very sudden and very violent happened," said William Waldock, who teaches accident investigation at Embry-Riddle Aeronautical University in Prescott, Ariz.

Malaysia had dispatched 15 planes and nine ships to the search area. The U.S. Navy sent a warship, the USS Pickney, which was conducting training and maritime security operations off the South China Sea.
The guided-missile destroyer is carrying two MH-60R helicopters that can be equipped for search and rescue efforts. The U.S. is also sending a surveillance plane, while Singapore said it would send a submarine and a plane. China and Vietnam were also sending aircraft to help in the search.

It is not uncommon for it to take several days to find the wreckage of an aircraft floating on the ocean. Locating and then recovering the flight data recorders, vital to any investigation, can take months or even years.

The airline said in a statement that it is currently notifying next-of-kin about the situation. "Our thoughts and prayers are with all affected passengers and crew and their family members," Yahya said.

Asked whether terrorism was suspected, Malaysian Prime Minister Najib Razak said, "We are looking at all possibilities, but it is too early to make any conclusive remarks."
"We are extremely worried,'' Chinese Foreign Minister Wang Yi told reporters in Beijing. "We are doing all we can to get details. The news is very disturbing. We hope everyone on the plane is safe."

Vietnamese website VN Express said a Vietnamese search and rescue official reported that signals from the plane were detected about 140 miles southwest of Vietnam's southernmost Ca Mau province. A Vietnam rescue official later denied the report.

"We have been seeking but no signal from the plane yet," Pham Hien, director of a Vietnam maritime search and rescue coordination center in Vung Tau, told Reuters.

China's state-run news agency Xinhua reported the plane was lost in airspace controlled by Vietnam, and never made contact with Chinese air traffic controllers. There have been no reports of a plane crashing into Chinese waters, and China is assisting the airline in its search for the plane.

Malaysian Transport Minister Hishammuddin Hussein also denied a Vietnamese state media report that the plane had crashed off south Vietnam, saying the government had not identified a crash scene.

The plane "lost all contact and radar signal one minute before it entered Vietnam's air traffic control," Lt. Gen. Vo Van Tuan, deputy chief of staff of the Vietnamese army, said in a statement issued by the government.
The airline says the plane's pilot is Captain Zaharie Ahmad Shah, a 53-year-old who has been with the airline for over 30 years. The plane's first officer is Fariq Ab.Hamid, a 27-year-old who joined the airline in 2007. Both are Malaysians.

At Beijing's airport, authorities posted a notice asking relatives and friends of passengers to gather at a hotel about nine miles from the airport to wait for further information, and provided a shuttle bus service. A woman wept aboard the shuttle bus while saying on a mobile phone, "They want us to go to the hotel. It cannot be good!"

Zhai Le was waiting for her friends, a couple, who were on their way back to the Chinese capital on the flight. She said she was very concerned because she hadn't been able to reach them.

Relatives and friends of passengers were escorted into a private area at the Lido Hotel, and reporters were kept away. A man in a gray hooded sweatshirt later stormed out complaining about a lack of information. The man, who said he was a Beijing resident but declined to give his name, said he was anxious because his mother was on board the flight with a group of 10 tourists.

"We have been waiting for hours," he said. "And there is still no verification."

In Kuala Lumpur, family members gathered at the airport, but were kept away from reporters.

"Our team is currently calling the next of kin passengers and crew. Focus of the airline is to work with the emergency responders and authorities and mobilize its full support," Jauhair, said.

"Our thoughts and prayers are with all affected passengers and crew and their family members," he said.

Fuad Sharuji, Malaysia Airlines' vice president of operations control told CNN that the plane was flying at an altitude of 35,000 feet when it disappeared and that the pilots had reported no problem with the aircraft.

Malaysia Airlines has 15 Boeing 777-200 jets in its fleet of about 100 planes. The state-owned carrier last month reported its fourth straight quarterly loss.

The 777 had not had a fatal crash in its 20 year history until the Asiana Airlines crash in San Francisco in July 2013.

Boeing said on its Twitter account it is monitoring the situation, and "our thoughts are with everyone on board."

Via: Fox News' Catherine Herridge and Dan Gallo and The Associated Press contributed to this report