KUALA LUMPUR, Malaysia - Malaysian police on Sunday were examining a flight simulator belonging to one of the pilots of the missing jetliner and investigating engineers who worked on the plane, sharpening the probe into the jet's disappearance after authorities revealed it was a deliberate act.
The government said police searched the homes of both of the plane's pilots on Saturday, but did not say whether it was the first time officers had done so since the flight went missing more than a week ago with 239 people aboard en route to Beijing from Kuala Lumpur.
Authorities were trying to narrow down the search for the plane, which satellite data shows could have kept flying as far north as Central Asia or far into the southern Indian Ocean, posing awesome challenges for efforts to recover the aircraft and flight data recorders vital to solving the mystery of what happened on board.
Given that the northern route would take the plane over countries with busy airspace, most experts say the person in control of the plane would more likely have chosen the southern route. The southern Indian Ocean is the world's third-deepest and one of the most remote stretches of water in the world, with little radar coverage. The wreckage might take months - or longer - to find, or might never be located.
Malaysia has asked for help from countries in South, Central and Southeast Asia for assistance in tracing the jet by providing satellite and radar data, the government said in a statement. It said that for now, both the northern and southern routes that the plane may have taken were being treated with "equal importance.''
There appeared to be some confusion over where to search as India, one of 12 countries contributing planes and vessels to the hunt, said it had stopped looking while waiting for confirmation from Malaysia on where to search. Australia, which looks onto the southern Indian Ocean from its west coast, said it had not been asked to begin searching there.
Malaysia's acting transport minister tweeted that he was in meetings to decide the "next course of action.''
In the first detailed account of what happened to the plane, Prime Minister Najib Razak said Saturday that someone severed communications with the ground and deliberately diverted Flight 370 back over the Malay Peninsula early on March 8.
The revelations raised questions over possible lapses by Malaysian authorities, including why the air force wasn't aware that a jetliner was flying over the country. It also triggered speculation over who on the plane was involved - and what motive they might have for flying away with an aircraft carrying a 12-person crew and 227 passengers.
If the pilots were involved in the disappearance, were they working together or alone, or with one or more of the passengers or crew? Did they fly the plane under duress or of their own volition? Did one or more of the passengers manage to break into the cockpit, or use the threat of violence to gain entry and then pilot the plane?
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Malaysian authorities have not ruled out any possibilities, and to establish what happened with any degree of certainty investigators will likely need to examine information, including cockpit voice recordings, from the plane's flight data recorders should the jet be located.
The government's statement on Sunday gave few details on the police investigation into the pilots. It said police searched the homes of both the pilot and the co-pilot and were examining an elaborate flight simulator belonging to Zaharie Ahmad Shah, the 59-year-old pilot.
Zaharie, who has children, had previously posted photos online of the flight simulator he built for his home using three large computer monitors and other accessories. Earlier this week, the head of Malaysia Airlines said this was not in itself cause for any suspicion.
Saying this was per normal procedure, the statement also said police were investigating engineers who may have had contact with the plane before it took off.
Najib said Saturday that investigators had a "high degree of certainty'' that one of the plane's communications systems - the Aircraft and Communications Addressing and Reporting System, or ACARS - was partially disabled before the plane reached the east coast of Malaysia. Shortly afterward, someone on board switched off the aircraft's transponder, which communicates with civilian air traffic controllers.
Malaysian officials and aviation experts said that whoever disabled the plane's communication systems and then flew the jet must have had a high degree of technical knowledge and flying experience, putting the pilots at the top of the list of possible suspects.
Najib confirmed that Malaysian air force defence radar picked up traces of the plane turning back westward, crossing over Peninsular Malaysia into the northern stretches of the Strait of Malacca. Authorities previously had said this radar data could not be verified.
The air force has yet to explain why it did not spot the plane flying over the country and respond. The search was initially focused on the Gulf of Thailand and the South China Sea, where the plane severed its communication links. That search has now ended.
"One thing that does bother me greatly is the fact that unidentified aircraft could navigate back over Malaysia and out to sea without a physical or material response to that fact,'' said Britain-based aviation security consultant Chris Yates. "They were not watching.''
Not much is known publicly about the two pilots.
Zaharie, who joined Malaysia Airlines in 1981, had more than 18,000 hours of flying experience.
Co-pilot Fariq Abdul Hamid, 27, was contemplating marriage after having just graduated to the cockpit of a Boeing 777. He has drawn scrutiny after the revelation that he and another pilot invited two female passengers to sit in the cockpit during a flight in 2011.
Neighbours and friends interviewed this week said Fariq played futsal, a modified form of soccer popular in Southeast Asia, with neighbourhood youngsters, and that he paid for their sports shirts.
Zaharie was known for cooking food for community events.
Associated Press writers Chris Brummitt and Jim Gomez contributed to this report from Kuala Lumpur. AP writer Didi Tang, video producer Aritz Parra and news assistant Henry Hou contributed from Beijing. AP writer Joan Lowy contributed from Washington.