The investigation into the disappearance of the Malaysia Airlines jet with 239 on board is now focused on the crew and passengers.
Malaysian authorities said on Sunday that police have searched the homes of the two pilots and are examining an elaborate flight simulator taken from one of them. Authorities are also investigating engineers who may have had contact with the plane before it left Kuala Lumpur.
A full-scale criminal investigation was triggered when Malaysian Prime Minister Najib Razak said Saturday there is a "high degree of certainty" that someone who knew what he was doing deliberately turned off the communications systems.
The prime minister said the last of the systems were switched off just before the jet turned westward, away from its flight path.
Najib stopped short of saying the plane was hijacked and said investigators are looking at all scenarios.
The search for Malaysia Airlines Flight 370 now ranges from Kazakhstan to the southern Indian Ocean. Investigators say the plane had enough fuel to fly for several hours after disappearing from radar on March 8.
The missing Boeing 777 was flying from Kuala Lumpur to Beijing when it disappeared. About two-thirds of the people on board were Chinese. Other passengers included Europeans and Americans.