Australia will lead a search of the remote southern Indian Ocean for a missing Malaysian airliner, amid mounting evidence the plane's disappearance was a meticulously planned act of sabotage or hijacking.
No trace of flight MH370 with 239 people aboard, including two New Zealanders, has been found since it vanished about an hour after takeoff on 8 March. Investigators believe the plane was diverted by someone with deep knowledge of the plane and of commercial navigation.
Satellite data suggests that the jet could be anywhere in either of two vast arcs: one stretching from northern Thailand to the borders of Kazakhstan and Turkmenistan, or a southern arc from Indonesia into the Indian Ocean west of Australia. The number of countries searching has nearly doubled from 14 to 25.
Australia already has two Orion aircraft looking for the plane. Prime Minister Tony Abbott said on Monday that he had spoken to Malaysian leader Najib Razak and ordered more assistance. "He asked that Australia take responsibility for the search in the southern vector, which the Malaysian authorities now think was one possible flight path for this ill-fated aircraft."
The Chinese Foreign Ministry, meanwhile, called on Malaysia to "immediately" expand and clarify the scope of the search. About two-thirds of the passengers on board the flight were Chinese.
Malaysian police revealed on Monday they are investigating Mohd Khairul, a 29-year-old flight engineer who was a passenger on the plane, as well as other passengers and crew. "The focus is on anyone else who might have had aviation skills on that plane," a senior police official with knowledge of the investigations told Reuters.
Investigators are trawling through the backgrounds of the pilots, crew and ground staff who worked on the missing Boeing 777-200ER for clues as to why someone on board flew it hundreds, or perhaps thousands, of miles off course.
Prime Minister Razak said on Saturday that evidence pointed to a deliberate diversion of the flight, given the controlled way it was apparently turned around and flown far to the west of its original route from Kuala Lumpur to Beijing.
A flight engineer is responsible for overseeing systems on a plane during flights to confirm they are working correctly and to make repairs if necessary. As an engineer specialising in executive jets, Mr Khairul would not necessarily have all the knowledge needed to divert and fly a large jetliner.
Mr Khairul had said he worked for a Swiss-based jet charter firm called Execujet Aviation Group, but the company declined to say whether it still employed him. The father-of-one has more than 10 years experience as a flight engineer.
Last words from cockpit
Malaysia's acting Transport Minister Hishammuddin Hussein confirmed on Sunday that the last words spoken from the cockpit - "all right, good night" - were uttered after someone on board had already begun disabling one of the plane's automatic tracking systems.
The informal handoff was spoken to air traffic controllers as the plane was leaving Malaysian-run airspace. It went against standard radio procedures, which would have called for him to read back instructions for contacting the next control centre and include the aircraft's call sign, Hugh Dibley, a former British Airways pilot and a Fellow of the Royal Aeronautical Society, told Reuters.
Malaysian authorities believe that as the plane crossed the country's north-east coast and flew across the Gulf of Thailand someone on board shut off its communications systems and turned sharply to the west.
Electronic signals the plane continued to exchange periodically with satellites suggest it could have continued flying for nearly seven hours after flying out of range of Malaysian military radar off the northwest coast, heading towards India.
The plane had enough fuel to fly for about eight hours, Malaysia Airlines' chief executive Ahmad Jauhari Yahya said. Investigators are trying to obtain more radar and satellite data from any of the countries that flight MH370 may have passed over.
A New Zealand pilot says that staff on the ground should have known if the missing plane had a catastrophic failure within an hour of losing contact.
Sam Savill, a Taiwan-based pilot who flies the same route as flight MH370, told Radio New Zealand's Checkpoint programme on Monday it would have been fairly obvious if the plane had crashed, because debris would have been found in the area where contact was lost.
Investigators believe the plane was taken off course by someone with a knowledge of aircraft, but Mr Savill said standard procedure in a hijacking is to not let anyone into the cockpit, which deepens the mystery further.
Pilots' homes searched
Police on Saturday searched the homes of the captain, 53-year-old Zaharie Ahmad Shah, and first officer Fariq Abdul Hamid, 27, in middle-class suburbs of Kuala Lumpur close to the international airport.
An experienced pilot, Mr Zaharie has been described by current and former co-workers as a flying enthusiast who spent his days off operating a life-sized flight simulator he had set up at home.
Police said investigators have taken the flight simulator for examination by experts. Earlier, a senior police official told Reuters the flight simulator programmes were closely examined and appeared to be normal ones that allow players to practice flying and landing in different conditions.
Police said that investigators had found no links between Mr Zaharie, a father of three grown-up children and a grandfather, and any militant group.
Friends and families of the pilots have expressed disbelief at the possibility that they could have been involved in the plane's disappearance.