Criminal probe under way in Malaysia plane drama

Saturday's startling revelations that the Boeing 777's communications systems had been manually switched off before the jet veered westward and flew on for hours raised more perplexing and deeply troubling questions about the fate of the plane and its 239 passengers and crew.

Briefing the press on Saturday, Prime Minister Datuk Seri Najib Tun Razak declined to use the word hijack, but said the new data suggesting a "deliberate action" by someone on board meant investigators had "refocused their investigation into crew and passengers".

For anguished relatives, the news was a double-edged sword -- holding out the slim hope that hijackers had landed the plane somewhere, while ushering in another agonising open-ended waiting period.

Relatives of Bob and Cathy Lawton, a missing Australian couple, said they were horrified by the notion of a drawn-out hijack ordeal.

"That's one of the worst things I could have hoped for," Bob's brother David Lawton told News Limited newspapers.

"Even if they are alive, what did they have to put up with?"

He said the family was struggling to come to terms with the idea that the couple might never come home and trying not to lose hope.

"We have hopes and dreams that something might come, but at the moment we just don't know. It's all up in the air."

The scope for speculation is as broad as the new search area that stretches from Kazakhstan to the southern Indian Ocean.

Expert opinion that disabling the communications system required specialist knowledge of the Boeing 777 has intensified scrutiny of Captain Zaharie Ahmad Shah and his First Officer, Fariq Abdul Hamid.

Scott Hamilton, managing director of US-based aerospace consultancy Leeham Co, said Najib's refusal to confirm a hijacking was telling.

"It sounded to me that the pilots haven't been ruled out. He was saying don't focus only on hijackers," Hamilton said.

Malaysian media reported that investigators had gone to the homes of both pilots on Saturday, although police refused to confirm.

Friends and colleagues of both men have testified to their good character, but questions have been raised over a flight simulator Zaharie had built at home, even though aviation commentators have said this is not uncommon.

Fariq's record was queried after a woman said he had allowed her and a friend to ride in the cockpit of a separate flight.

The alternative scenario that the cockpit was taken over or the pilots coerced, opens a Pandora's Box of possibilities as to who might be involved and with what motive.

Two passengers who boarded the plane with stolen EU passports have been identified as Iranians by Interpol, who said they were most likely illegal immigrants who did not fit terrorist profiles.

The fact that most of the passengers on board the Beijing-bound flight were Chinese has raised the possibility of involvement by militants from China's Muslim ethnic Uyghur minority.

Security experts warned against jumping to conclusions on the basis of partial, flimsy evidence.

"We have to keep in mind that it's still early in the investigation, even though we're a week out from the plane taking off," said Anthony Brickhouse, a member of the International Society of Air Safety Investigators.

"We still really don't have a lot of evidence to go on. We don't have any wreckage, we don't have the plane itself, we don't have a lot of electronic data from the aircraft."

The search is now focused on two flight corridors -- a northern one stretching from northern Thailand to Kazakhstan and a southern zone from Indonesia towards the southern Indian Ocean.

The last satellite communication from the plane on March 8 came after it had been in the air almost eight hours -- around the time the airline has said it would have run out of fuel.

Several analysts favoured a route along the southern corridor over the ocean, saying the northern one would have required the plane to travel undetected through numerous national airspaces in a strategically sensitive region.

"I just can't think of a scenario where this aircraft is sitting on a runway somewhere," said Brickhouse.

Hamilton said a crash in the ocean was the likeliest scenario and one that presented a daunting search and recovery challenge.

"Any floating debris will be widely dispersed and the main debris on the sea floor," he said.