The turn that diverted the missing Malaysian Airlines plane off its flight path was programmed into the aircraft's computer navigation system, probably by someone in the cockpit, the New York Times reported late Monday.
That reinforces the increasing belief among investigators that the aircraft was deliberately diverted, the newspaper said, quoting US officials.
Rather than manually operating the plane's controls, whoever altered Flight 370's path typed seven or eight keystrokes into a computer situated between the captain and the co-pilot, according to officials.
The computer is called the Flight Management System. It directs the plane from point to point specified in the flight plan submitted before a flight.
It is not clear whether the plane's path was reprogrammed before or after it took off, the Times said.
Flight 370 vanished on March 8 with 239 people aboard a flight from Kuala Lumpur to Beijing.
Malaysia said Saturday it believed the plane had been diverted because its transponder and other communications devices had been manually turned off several minutes apart.
But confusion has taken hold over the timeline of events before ground controllers lost contact with the aircraft.
Malaysia on Monday said it was the co-pilot Fariq Abdul Hamid who was the last person in the cockpit to speak to ground control.
Identifying the voice had been deemed crucial because officials initially said the words were spoken after one of the Boeing's two automated signalling systems -- Aircraft Communications Addressing and Reporting System (ACARS) -- had been manually disabled.
But Malaysia Airlines director Ahmad Jauhari Yahya contradicted that chronology, saying that the ACARS could have been switched off before or after Fariq spoke.
The Times said the changes made to the plane's direction through the Flight Management System were reported back to a maintenance base by ACARS, according to an American official.
This showed the reprogramming happened before the ACARS stopped working, at about the same time that oral radio contact was lost and the airplane's transponder also stopped. This fuels suspicions that foul play was involved in the plane's disappearance.
Investigators are scrutinizing radar tapes from when the plane first departed Kuala Lumpur because they believe the tapes will show that after the plane first changed its course, it passed through several pre-established "waypoints", which are like virtual mile markers in the sky, the Times said.
That would suggest the plane was under control of a knowledgeable pilot because passing through those points without using the computer would have been unlikely, it added.