The plane's disappearance has baffled investigators and aviation experts. It vanished from civilian air traffic control screens off Malaysia's east coast less than an hour after taking off from Kuala Lumpur.

Malaysian authorities believe that, as the plane crossed the northeast coast and flew across the Gulf of Thailand, someone on board shut off its communications systems and turned west.

That has focused attention on the crew. Malaysian police are trawling through the backgrounds of the pilots, flight and ground staff for any clues to a possible motive in what they say is now being treated as a criminal investigation.

Asked if pilot or co-pilot suicide was a line of inquiry, Hishammuddin said: "We are looking at it." But he added it was only one of the possibilities under investigation.

Police special branch officers searched the homes of the captain, 53-year-old Zaharie Ahmad Shah, and first officer, 27-year-old Fariq Abdul Hamid, in middle-class suburbs of Kuala Lumpur close to the international airport on Saturday.

Among the items taken for examination was a flight simulator Zaharie had built in his home.

A senior police official familiar with the investigation said the flight simulator programmes were closely examined, adding they appeared to be normal ones that allow users to practise flying and landing in different conditions.

A second senior police official with knowledge of the investigation said they had found no evidence of a link between the pilot and any militant group.

"Based on what we have so far, we cannot see the terrorism link here," he said. "We looked at known terror or extremist groups in Southeast Asia. The links are not there."

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	Video: Officials remain puzzled Tension mounted as the search for the missing Malaysian airplane continued.