The pilots on the missing Malaysia Airlines plane did not ask to fly together, authorities announced as they relaunched a major search operation.
New details have been revealed about pilot Zaharie Ahmad Shah and co-pilot Fariq Abdul Hamid's personal and religious backgrounds.
Their homes have been searched as investigators try to find out what happened to flight MH370 carrying 239 people.
The plane vanished around 40 minutes into its flight from Kuala Lumpur to Beijing.
Investigators say the jet was deliberately diverted and its tracking devices disabled.
Satellite data suggested the plane flew for at least seven hours - more than six hours after the last radio contact - and it could have reached north into Central Asia or much further south in the Indian Ocean.
Mr Zaharie, who has more than 18,000 hours flying experience and joined Malaysia Airlines in 1981, is known to be an avid aviation enthusiast.
Police are examining a flight simulator found at his home and are also investigating engineers who might have had contact with the jet.
Malaysia Transport Minister Hishammuddin Hussein told a news conference: "Officers visited the home of the pilot. They spoke to family members, and experts are examining the pilot's flight simulator.
"The police also visited the home of the co-pilot. According to Malaysia Airlines, the pilot and co-pilot did not ask to fly together on MH370."
A fresh emphasis has been placed on the pilots' psychological state, family life and connections.
Investigators are convinced the plane 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 said.
A series of claims have been made about 53-year-old Mr Zaharie, who has attracted a greater focus than 27-year-old co-pilot Mr Fariq.
Postings on Mr Zaharie's Facebook page suggest he was a politically active opponent of the coalition that has ruled Malaysia for 57 years since the country's independence.
Just hours before the plane took off, 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.
He was found guilty after an earlier acquittal was overturned and it has been reported Mr Zaharie was at his trial this month.
There has been a suggestion that Mr Zaharie was upset at Mr Ibrahim's conviction, but the opposition leader's office told Sky News that is entirely implausible.
Asked if Mr Zaharie's background as an opposition supporter was being examined, a senior police officer would only say: "We need to cover all our bases."
Other aviation experts say Mr Zaharie having a flight simulator at his home is not unusual - but it has been another focus for investigators.
The senior police official said: "With Zaharie, the flight simulator games were looked at closely."
He said they appeared to be normal programmes that allow players to practise flying and landing in different conditions.
Co-pilot Mr Fariq recently graduated to the cockpit of the Boeing 777.
His behaviour was criticised three years ago, when pictures emerged of him inviting two female passengers to sit in the cockpit during a flight.