Malaysia Probes Passenger Backgrounds for Clues on Missing Flight

  Malaysia is investigating whether any passengers or crew aboard a missing airliner had personal or psychological problems that might explain its disappearance, along with the possibility of a hijack, sabotage or mechanical failure, police said on Tuesday.

  A massive search operation for the Malaysia Airlines Boeing 777-200ER is in its fourth day, with no trace yet of the aircraft or the 239 people on board, one of the most baffling mysteries in aviation history.

  Flight MH370 left Kuala Lumpur for Beijing early on Saturday morning, vanishing from radar screens about an hour after take-off over the sea separating Malaysia from the southern tip of Vietnam. Adding to the puzzle, Malaysian military radar tracking suggested it may have turned back from its scheduled route.

  There was no distress signal or radio contact indicating a problem and, in the absence of any wreckage or flight data, police have been left trawling through passenger and crew lists for potential leads.

  The fact that at least two passengers on board had used stolen passports, confirmed by Interpol, has raised suspicions of foul play. But Southeast Asia is known as a hub for false documents that are also used by smugglers, illegal migrants and asylum seekers.

  Police chief Khali said one of the men had been identified as a 19-year-old Iranian, who appeared to be an illegal immigrant. The identity of the other was still being checked.

  Both men entered Malaysia on Feb 28, at least one from Phuket, in Thailand, eight days before boarding the flight to Beijing, Malaysian immigration chief Aloyah Mamat told the news conference. Both held onward reservations to Western Europe.

  Police in Thailand, where the passports were stolen and the tickets used by the two men were booked, said they did not think they were linked to the disappearance of the plane.

  The massive search for the plane has drawn in navies, military aircraft, coastguard and civilian vessels from 10 nations.

  The search was widened on Tuesday to cover a larger swathe of the shallow waters of the Gulf of Thailand and South China Sea around the last known position of the plane.

  But searches were also being conducted on the western coast of Malaysia and northwest towards the much deeper Andaman Sea - based on a theory that the plane may have flown on for some time after deviating from its flight path.

  Neither Malaysia's Special Branch, the agency leading the investigation, nor spy agencies in the United States and Europe, have ruled out the possibility of a hijack or bombing.

  But Malaysian authorities have indicated the evidence so far does not strongly back an attack as a cause for the aircraft's disappearance, and that mechanical or pilot problems could have led to the apparent crash, U.S. government sources said.

  The United States extensively reviewed imagery taken by spy satellites for evidence of a mid-air explosion, but saw none, a U.S. government source said.

  Vietnam said it was allowing ships and planes from Malaysia, Singapore, China and the United States to enter its waters to search for the plane.

  About two-thirds of the 227 passengers and 12 crew now presumed to have died aboard the plane were Chinese. Other nationalities included 38 Malaysians, seven Indonesians, six Australians, five Indians, four French and three Americans.

  China has deployed 10 satellites using high-resolution earth imaging capabilities, visible light imaging and other technologies to "support and assist in the search and rescue operations", the People's Liberation Army Daily said on Tuesday.

  The Boeing 777 has one of the best safety records of any commercial aircraft in service. Its only previous fatal crash came on July 6 last year when Asiana Airlines Flight 214 struck a seawall on landing in San Francisco, killing three people.

  U.S. plane maker Boeing has declined to comment beyond a brief statement saying it was monitoring the situation.