Investigators are looking at the histories of Capt. Zaharie Ahmad Shah, 53, who has been flying for Malaysia Airlines since 1981 and co-pilot Fariq Abdul Hamid, 27, who just started flying a 777.
Zaharie had built his own flight simulator at home, unusual but not out of the norm.
Many aviation enthusiasts have similar setups; one Los Angeles flight attendant recreated a Pan Am first class cabin in his garage.
Investigators are now trying to restore files deleted from that simulator.
Why suspect the pilots? The plane's transponder stopped signaling its location to air-traffic controllers and other planes at the perfect moment: the handoff from Malaysia's controllers to those in Vietnam.
In the final radio contact from the plane, the co-pilot told Malaysian controllers "All right, good night.'' Vietnamese controllers were never contacted and the transponder shut off. The plane abruptly turned and then kept flying for up to seven hours.
The way several key communication and tracking devices in the cockpit were disabled — at different times — also places suspicion on the pilots.
The idea of pilots using a plane to commit suicide and mass murder is scary, taboo within the industry but not unprecedented.
A SilkAir crash in 1997 and an EgyptAir crash in 1999 are both believed to have been the result of deliberate actions by pilots.
