Investigators are increasingly certain that the missing Malaysia Airlines jet turned back across the Malay Peninsula after losing communication - and that someone with aviation skills was responsible for the unexplained change in course.
The revelation by a Malaysian government official involved in the probe added fuel to the theory that flight MH370 fell victim to foul play early last Saturday morning. "Somebody did something deliberate," said Mikael Robertsson, co-founder of FlightRadar24.
Robertsson said the transponder, which reports its position to ground-based radar, switched off 40 minutes into the flight, something that could happen only if it was turned off or if the plane was destroyed.
US network ABC also reported that US investigators believed the aircraft's data reporting system and the transponder shut down 14 minutes apart, suggesting the plane did not suffer a sudden catastrophic incident.
A US official said investigators were examining the possibility of "human intervention", adding the disappearance may be "an act of piracy".
Malaysian officials also acknowledged yesterday that the transponder disconnection could indicate a hijacking.
"It could have been done intentionally. It could have been done under duress. It could have happened as a result of an explosion," said Hishammuddin Hussein, Malaysia's acting transport minister.
The Malaysians said they were expanding their search towards India on the possibility that the plane - carrying 12 crew and 227 passengers - had been diverted there, but that they would also continue their search closer to the original flight path in the South China Sea.
"The aircraft is still missing, and the search area is expanding," Hishammuddin said.
Meanwhile,a British satellite communications company confirmed on Friday that it had recorded electronic “keep alive” ping signals from the plane after it disappeared, and said those signals could be analyzed to help estimate its location.
The information from the company, Inmarsat, could be a turning point for Malaysian investigators and foreign experts drafted to assist with the hunt for the jet.
Inmarsat equips ships and airplanes with satellite systems systems, and had equipment aboard the Malaysia Airlines Boeing 777, said David Coiley, the vice president of the company in charge of the aviation business. The equipment automatically communicates with satellites, much as a mobile phone would automatically connect to a network after passing through a mountain tunnel, he said.
In a further indication that the plane was under piloted control, the New York Times reported that Malaysian military radar data showed the jet climbed to 45,000ft, above the approved altitude limit for a Boeing 777-200, soon after its last known position, after making a turn to the west.
It said there were indications that MH370 descended to 23,000ft on the approach to Penang, one of Malaysia's largest and most densely populated islands. Then came another turn, this time north-west on a trajectory that took it over the Strait of Malacca and out towards the Indian Ocean.
Two unnamed sources said data gleaned from military radar showed that an unidentified aircraft seemed to follow a commonly used navigational route northwest of Malaysia on the night the flight disappeared. That course - into the Andaman Sea and towards the Bay of Bengal - could only have been set deliberately, either by flying the Boeing 777 jet manually or by programming the autopilot.
However, Indian officials questioned the expansion of the search towards the Andaman Islands. An unidentified navy official said he was confident the Boeing 777 was not in the area, saying radar coverage would detect the plane.
Malaysia is also working with US investigators to establish if there was any satellite information that could help locate the flight. That followed a report by The Wall Street Journal that a satellite received intermittent "pings" from the aircraft - with the last detected over water.
"Whatever they have [they] will share with us," Azharuddin Abdul Rahman, director general of Malaysia's Civil Aviation Authority, said.
US officials said the jet was emitting signals to satellites for hours after its last contact with air traffic control. That opened the possibility that one of the pilots, or someone with flying experience, wanted to hijack the plane for some later purpose, kidnap the passengers or commit suicide by plunging the jet into the sea.
Mike Glynn, a committee member of the Australian and International Pilots Association, said he considered pilot suicide to be the most likely explanation for the disappearance, as was suspected in a SilkAir crash in 1997 and an EgyptAir crash in 1999.
"A pilot rather than a hijacker is more likely to be able to switch off the communications equipment," Glynn said. "The last thing that I, as a pilot, want is suspicion to fall on the crew, but it's happened twice before."
Watch: Aviation expert considers missing flight MH370 theories
China, which has the most citizens aboard the plane, added another naval ship to the search in the Gulf of Thailand and redeployed a civilian government ship to the Strait of Malacca.
China's deployment to the search and rescue operation, however, has been hampered by limited access to data from Malaysian authorities, said an aviation expert with links to the Chinese government who requested anonymity. The source said that US officials had direct access to details.
Thirteen nations are still searching around the clock, with 48 aircraft and 57 ships.
Some 23 ships were deployed in the Strait of Malacca, Indian Ocean and Andaman Sea. To the east, more than 30 vessels continued looking along the presumed flight path in the South China Sea between Malaysia and Vietnam.
Watch: Hunt for missing jets spreads to Indian Ocean
Meanwhile, a team of seismologists with the University of Science and Technology of China in Hefei said that a slight tremor had occurred on the sea floor between Vietnam and Malaysia last Saturday, the day the plane disappeared.
Professor Fu Liyun , seismologist with the Chinese Academy of Sciences' Institute of Geology and Geophysics, said the occurrence might be consistent with a plane crashing into the sea, which would produce "enormous shock waves".
Reuters, Associated Press, McClatchy Tribune, Bloomberg with Danny Lee, Kristine Kwok, Adrian Wan in Kuala Lumpur, Stephen Chen and Andrea Chen in Beijing