The flight computer on missing Malaysia Airlines flight MH370 was "manually overwritten", investigators have said.
The plane carrying 239 passengers and crew disappeared last week after diverting from its planned flight path from Kuala Lumpur to Beijing.
It has since been discovered that the plane made several erratic course corrections which have led investigators to dramatically widen the "search corridors" where evidence of its fate could be found.
Above: Students stand next to a giant mural featuring missing Malaysia Airlines flight MH370
Search efforts are focused on two corridors - one stretching from the border of Kazakhstan and Turkmenistan to northern Thailand, and another from Indonesia to the Indian Ocean.
It is overwhelmingly likely that the plane ditched or broke up above the Pacific or Indian ocean, experts believe. But no remains of the aircraft have yet been found.
Now investigators say that they are sure the course adjustments made by the plane were manually programmed by someone in the plane's cockpit.
Specifically, it is thought that at least the first turn to the West that the plane took must have been carried out by someone knowledgeable of the Boeing 777-200ER system, or a similar plane.
The course change was not made via the flight controls, but input with seven or eight keystrokes into a computer between the captain and first officer.
The Flight Management System is used to direct the plane between waypoints on its journey. It is possible, officials said, that it was reprogrammed before the plane took off.
According to the Sydney Morning Herald the finding has refocused attention on the pilot or first officer, and raised greater suspicions of "foul play". US aviation experts have said it is wildly unlikely that a passenger could have reprogrammed the computer, despite speculation that the plane could have been "hacked", a theory proposed by a former Home Office official.
It is known that the flight MH370 reported its status to the Aircraft Communications Addressing and Reporting System (Acars) after the reprogramming had taken place, but that system stopped functioning soon after.
Meanwhile the frustation of families and loved ones aboard MH370 has continued to escalate, with some reportedly threatening a hunger strike unless they are told the "truth" about the flight.