The disappearance of the Malaysian Boeing has baffled investigators, aviation experts and internet sleuths.
Police are combing through the personal, political and religious backgrounds of pilots and crew of a missing Malaysian jetliner, a senior officer said on Sunday, trying to work out why someone aboard flew the plane hundreds of kilometres off course.
No trace of the Malaysia Airlines Boeing 777-200ER has been found since it vanished on March 8 with 239 people on board, but investigators believe it was diverted by someone who knew how to switch off its communications and tracking systems.
"We are not ruling out any sort of motivation at the moment," a senior police official with knowledge of the investigation told Reuters.
Satellite data revealed by Malaysia's prime minister on Saturday suggests the plane could be anywhere in either of two arcs: one stretching from northern Thailand to the border of Kazakhstan and Turkmenistan, or a southern arc heading from Indonesia to the vast southern Indian Ocean.
A source familiar with official US assessments said it was thought most likely the plane had headed south into the Indian Ocean, where it would presumably have run out of fuel and crashed. Air space to the north is much busier, and the plane would likely have been detected.
As authorities desperately try to re-focus the multinational search, India said it was suspending operations around island chains north-west of the Malay Peninsula, at the request of Malaysian officials.
Indian defence officials said Malaysia wanted to reassess priorities. Malaysian officials coordinating the search could not be reached for comment.
The disappearance of Flight MH370 has baffled investigators, aviation experts and internet sleuths since the plane vanished from civilian air traffic control screens off Malaysia's east coast less than an hour after taking off from Kuala Lumpur en route to Beijing.
For relatives of those missing, the wait for any firm news has been agonising.
At a news conference on Saturday, Prime Minister Najib Razak said investigators believed somebody cut off the plane's communications reporting system, switched off its transponder and steered it west, far from its scheduled route.
Electronic signals it continued to exchange periodically with satellites suggest it could have continued flying for nearly seven hours after being last spotted by Malaysian military radar off the country's northwest coast.
Najib said that in light of the mounting evidence that the plane was deliberately diverted, the investigation into the aircraft's crew and passengers would be stepped up.
Within hours, special branch officers had 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.
An experienced pilot, Zaharie, has been described by current and former co-workers as a flying enthusiast who spent his off days operating a life-sized flight simulator he had set up at home.
"With Zaharie, the flight simulator games were looked at closely," the senior police official said, adding that they appeared to be normal programmes that allow players to practice flying and landing in different conditions.
Postings on his Facebook page suggest the pilot was a politically active opponent of the coalition that has ruled Malaysia for the 57 years since independence.
A day before the plane vanished, opposition leader Anwar Ibrahim was convicted of sodomy and sentenced to five years in prison, in a ruling his supporters and international human rights groups say was politically influenced.
Asked if Zaharie's background as an opposition supporter was being examined, the senior police officer would say only: "We need to cover all our bases."
Malaysia Airlines has said it did not believe Zaharie would have sabotaged the plane, and colleagues were incredulous.
"Please, let them find the aircraft first. Zaharie is not suicidal, not a political fanatic as some foreign media are saying," a Malaysia Airlines pilot who is close to Zaharie told Reuters. "Is it wrong for anyone to have an opinion about politics?"
Co-pilot Fariq was religious and serious about his career, family and friends said, countering news reports suggesting he was a cockpit Romeo who was reckless on the job.
Malaysia said the latest analysis of satellite data showed the last signal from the missing plane at 8.11am local time, almost seven hours after it turned back over the Gulf of Thailand and re-crossed the Malay peninsula.
The data did not show whether the plane was still flying or pinpoint its location at that time, presenting searchers with a daunting task. Seven hours' more flying time would likely have taken it to the limit of its fuel load.
Experts from the US Federal Aviation Authority and National Transportation Safety Board have been working with Malaysian authorities to analyse the data from geostationary satellites operated by Britain's Inmarsat.
India had been searching in two areas, one around the Andaman and Nicobar Islands and a second further west in the Bay of Bengal, both in the direction the plane was heading when it dropped off Malaysia's military radar at 2.15am local time.
Both searches have been suspended, but may resume, defence officials said on Sunday.
The Indian Ocean is one of the most remote places in the world and also one of the deepest, posing potentially enormous challenges for efforts to find wreckage or the flight voice and data recorders that are the key to solving the puzzle. - Reuters