The pilots of the missing Malaysian jet are at the center of a newly opened criminal investigation

(Image credit: Rahman Rosian / Getty Images)

last updated 8 January 2015

The mystery of missing Malaysia Airlines Flight 370 has moved from being simply a search operation to a criminal investigation, with authorities probing the flight crew's and passengers' backgrounds for a possible motive. The new phase of the investigation began shortly after Malaysian Prime Minister Najib Razak said Saturday that authorities determined "deliberate action" diverted the plane.

Malaysian authorities this weekend searched the homes of the plane's pilot, Zaharie Ahmad Shah, and co-pilot, Farq Ab Hamid, removing a flight simulator from Shah's residence for further examination. And a Malaysian official revealed Sunday that a signaling system onboard the plane was already turned off when Shah radioed air traffic controllers and reported that nothing was amiss. Meanwhile, U.S. intelligence officials told CNN they are "leaning toward the theory" that the flight crew was responsible for the plane's disappearance, though they haven't yet ruled out other possible explanations.