Last night sources told the Herald the pilots of the Malaysia Airlines jet had become the key suspects in the investigation into the plane's disappearance.
All airline staff or ground crew with links to the flight or its pilots are also being questioned, including some who work on the Kuala Lumpur-to-Auckland service.
And Malaysian police say they are examining a flight simulator belonging to the captain, Zaharie Ahmad Shah, 53, who is known to have spent time in New Zealand in 2012.
Video: Malaysia asks for data to find jet
On Saturday, it was confirmed that someone deliberately diverted Flight 370 and shut down its communications with the ground. The jet continued flying for six hours, but there has been no sign of it, its 227 passengers or 12 crew since.
Read more of today's Herald Flight 370 coverage:
• Was it pilot suicide?
• 9/11 type hijack of missing jet probed
• Missing plane could be off coast of Perth
Officials say the Boeing 777 was taken over by someone with intimate knowledge of the cockpit.
Based on data collated by the British company Inmarsat's satellite network, at that point the plane was on one of two possible arcs - one stretching north from Thailand to Kazakhstan and crossing more than 10 countries, and one to the south over Indonesia and out across the southern Indian ocean.
Experts have said the aircraft could have been on the ground when it sent its satellite signals.
Boeing 777s need a runway of at least 5,000ft long, limiting the number of possible sites within the 2,200 nautical mile-radius it is believed the plane could have flown from its last known position.
Last night sources in Kuala Lumpur assisting with the investigation told The Independent that full diplomatic permissions were being sought in order to rule out the theory that the plane could have flown to areas of Afghanistan and Pakistan that are not under government control.
Large areas of the southern half of Afghanistan are ruled by the Afghan Taliban, while some areas of north-west Pakistan, adjacent to or near to the Afghan border, are controlled by the Pakistani Taliban.
A spokesman for Malaysia Airlines said: "These are matters for the jurisdiction of those regions and Malaysia's armed forces and department of civil aviation. In regard to Pakistan and Afghanistan, we cannot explore those theories without permission. We hope to have that soon."
For a commercial plane to pass undetected through these regions, which are highly militarised with robust air defence networks, many run by the US military, would require a combination of extremely sophisticated navigation, brazen audacity and security failure by those monitoring international airspace. However, with so little known about the fate of the plane, and the investigation growing in scale every day, it is yet another line of enquiry that remains impossible to rule out. On Sunday Pakistani civil aviation officials said they had checked their radar recordings and found no sign of the missing jet.
Investigation focuses on pilots
Authorities have been looking closely into Captain Shah and co-pilot Fariq Abdul Hamid, 27. The homes of both have been searched by authorities, including the FBI, and evidence, including laptops, has been seized.
A senior source with intimate knowledge of the investigation spoke to the Herald on condition of anonymity. He said the calm manner in which one of the flight crew said his last words, "All right, good night" - made after the aircraft communications and reporting system (Acars), which sends information about the plane's location to air traffic control, was deliberately switched off - had made the pilots a focus of the investigation.
"There was no commotion and we do not believe there was anyone else in the cockpit," he said.
Malaysian Prime Minister Najib Razak said investigators now had a "high degree of certainty" the Acars was disabled before the jet reached the east coast of Malaysia.
Shortly after, someone on board switched off the transponder, which communicates with civilian air traffic control.
The Herald source said the main objective of the investigation was not about "who's at fault" but "where is the aircraft".
"The searches at the homes of the captain and co-pilot [were] to see if there was anything that could give investigators a clue where the plane went," the source said. "How it happened, who is to blame ... that is not a priority at this stage."
He said there was no evidence the jet was hijacked because there had been no ransom demands.
Video: Search for jet expands amid signs it flew on
He also confirmed that Captain Shah had links with Malaysian Opposition leader Anwar Ibrahim and investigators are looking at whether the disappearance could be politically related.
Politically motivated?
Just hours before the flight departed, Captain Shah reportedly attended the end of Ibrahim's trial on charges relating to homosexuality. The politician was jailed for five years.
Speculation is rife Captain Shah, an "obsessive" supporter of Ibrahim, was angry at the outcome of the trial and took the plane as a protest.
But the Malaysian coalition Pakaten Rakyat dismissed the reports that Shah was a "political fanatic", calling the report "wild speculation".
A Malaysia Airlines pilot who is close to Shah also told Reuters. "Is it wrong for anyone to have an opinion about politics?"
"Please, let them find the aircraft first. Zaharie is not suicidal, not a political fanatic."
Could plane have landed somewhere?
A former intelligence officer with the CIA says the disappearance of Malaysian flight MH370 has been more skilfully executed than the 9/11 attack.
There's speculation that the plane might have landed somewhere.
Mike Scheuer told Newstalk ZB's Rachel Smalley it appears to be even more precise than 9/11.
"It's not evident that it was a suicide mission. Perhaps they have other uses for the plane if it's a terrorism attack.
"Perhaps they're going to try bargain with the West for the release of some al-Qaeda people in return for releasing the passengers who were on the plane.''
He says if it was an act of terrorism, there could be a rogue plane out there.
"Once their plane is down somewhere you can repaint it, you can put a different number on the fuselage, and if you replace some of the equipment it won't give off the identifying signal that it would give off normally.
"And then you have kind of a wild card aircraft out there.''
Aviation expert Stephen Ganyard says the disappearance of the Malaysian Airline flight must have been planned, by people who knew exactly what they were doing.
"This had to have been a trained pilot, somebody had to know what they were doing.
"All these things occurred at the hand off between Malaysian and Vietnamese air traffic controllers.
"They knew that it was this dead zone in there, they knew that they had some time.''
Pilots' colleagues questioned
In his Facebook profile, Captain Shah is pictured on a ferry leaving downtown Auckland. It was posted in January 2012.
Malaysia Airlines' New Zealand manager, Dzulkifli Zakaraia, did not respond to calls about Captain Shah's time in New Zealand.
Kuala Lumpur-based crew and ground staff told the Herald that some of their colleagues who were linked to the flight or were friends of the pilots were also being questioned.
"From the questions the police were asking, it's as if they think it's an inside job," said one staffer.
She revealed some of those questioned had worked on Kuala Lumpur-Auckland flights, and serviced planes used for the route.
Pilots' houses searched
Police entered Mr Hamid's house about 1am yesterday (NZT) and left carrying two brown bags an hour later.
Captain Shah's house had been searched a few hours earlier.
It has been reported that he was separated from his wife, but the pair still lived at the family home where they raised three children.
It is understood Captain Shah's wife and children moved out of the house the day before the plane disappeared, and when police raided the property, only a maid was there.
- Additional reporting, UK Independent
Flight crew
Captain
* Zaharie Ahmad Shah
* Aged 53
* Separated, three children
* Joined Malaysia Airlines in 1981
* 18,365 flight hours
* Known as an avid flight buff
* Built own flight simulator in his home
Co-pilot
* Fariq Abdul Hamid
* Aged 27
* Unmarried
* 2763 hours of flight experience
* Had only recently started co-piloting the Boeing 777
* Previously invited two women passengers into the cockpit and smoked on an earlier flight to Phuket.
Three giveaway clues
Aviation safety experts say three pieces of evidence make it clear the jet was taken over by someone who knew how the plane worked.
Transponder
The plane's transponder - a signal that identifies the plane to radar - was shut off about an hour into the flight. Someone in the cockpit would have had to turn a knob with multiple selections to the off position while pressing down, said John Goglia, a former member of the US National Transportation Safety Board. A pilot would know how to do it, he said, but it could also be learned on the internet.
Acars
Part of the Boeing 777's Aircraft Communications Addressing and Reporting System (Acars) was shut off. The system is used to send messages to the airline's home base. The information part of the system was shut down, but not the transmission part. In most planes, the information part of the system could be shut down by hitting cockpit switches in sequence, then using a computer keypad, said Goglia. A pilot would know how to do that, but it could also be discovered through research. But access to the other part of the Acars was in an electronics bay beneath the cockpit and a pilot wouldn't know how to do it. It stayed on.
Guided flight
After the transponder was turned off and civilian radar lost track of the plane, Malaysian military radar was able to track the plane as it turned west along a known flight route for several hundred kilometres. To follow that course, someone had to be guiding the plane, Goglia said.
- AP
