A Malaysian government official tells The Associated Press that investigators have concluded that one of the pilots or someone else with flying experience hijacked the missing Malaysia Airlines jet. 

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Investigators trying to solve the disappearance of a Malaysia Airlines jetliner have concluded that one of the pilots or someone else with flying experience hijacked the missing Boeing 777 and steered it off course, according to a Malaysian government official.

The official, who is involved in the investigation, told The Associated Press that no motive has been established, and it is not yet clear where the plane was taken. The official spoke on condition of anonymity because he was not authorized to brief the media.

The official said that hijacking was no longer a theory. "It is conclusive."

The jet's communication with the ground was severed under one hour into a flight March 8 from Kuala Lumpur to Beijing. Malaysian officials have said radar data suggest it may have turned back and crossed back over the Malaysian peninsula westward, after setting out toward the Chinese capital.

A senior U.S. official told Fox News on Friday that the search effort will broaden deep into the Indian Ocean, based on new intelligence assessments that there is a "higher probability" the aircraft went down in that region, a senior U.S. official told Fox News.  

As a consequence of the shared U.S.-Malaysian intelligence assessments, it is understood that the U.S. Navy destroyer USS Kidd will expand its search into a southern quadrant of the ocean, while Indian authorities will cover a northern quadrant.

The development comes as authorities speculate that the disappearance may have been an "act of piracy,” and more evidence suggests the plane was diverted by a skilled pilot before it vanished, U.S. and Malaysian officials familiar with the investigation said Friday.

Investigators trying to piece together what happened to the Malaysia Airlines jetliner carrying 239 people are increasingly certain that someone with aviation skills was controlling the plane when it began purposely flying hundreds of miles off course Saturday.

A Malaysian government official involved in the mysterious case said only a skilled person could navigate the Boeing 777 the way it was flown after its last confirmed location over the South China Sea, the Associated Press reported.   

The official declined to be identified because he is not authorized to brief the media.

Key evidence for "human intervention" in the plane's disappearance is that contact with its transponder stopped about 12 minutes before a messaging system quit, an unidentified American official told the Associated Press. The official -- also not authorized to speak publicly -- said it's also possible the plane may have landed somewhere. 

ABC News  quoted two unidentified American officials as saying the U.S. believes the plane's data reporting system and transponder were shut down separately, at 1:07 a.m. and 1:21 a.m. Such a scenario would indicate the plane did not disappear due to some kind of catastrophic failure. 

A source familiar with the investigation but not authorized to speak on the record told Fox News that flight 370 continued to send "periodic pushes" of data after the transponder went dark for about four hours after contact was lost with the aircraft, suggesting the jet continued to fly. This was described to Fox News as signals data that, in isolation, would not provide location data. 

While the systems were no longer transmitting maintenance data, the satellite communication link was still active. Once an hour, the system sent out a “handshake” -- a form of reset, like a cell phone searching for an antenna tower.

The “handshake” allows the satellite to work out how much tilt or arc was needed to be in range of the plane's signal. It therefore provides a scope or range for the aircraft, but it does not provide altitude, speed or location.

If the plane had disintegrated during flight or had suffered some other catastrophic failure, all signals — the pings to the satellite, the data messages and the transponder — would be expected to stop at the same time.

Analysis of the Malaysia flight data suggests the plane diverted from its intended northeast route from Kuala Lumpur to Beijing and instead flew west, using airline flight paths normally taken to the Middle East and Europe, Reuters reported Friday.

This points to the theory that the plane was being flown by the pilots or possibly someone familiar with those routes, according to sources in the Reuters report .

Details such as these are leading investigators to sharpen their focus the possibility of sabotage, The Wall Street Journal reported late Friday.

Mike Glynn, a committee member of the Australian and International Pilots Association, said he considers pilot suicide to be the most likely explanation for the disappearance, as was suspected in a SilkAir crash during a flight from Singapore to Jakarta in 1997 and an EgyptAir flight from Los Angeles to Cairo 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."

"What we can say is we are looking at sabotage, with hijack still on the cards," said that source, a senior Malaysian police official.  

Malaysian police have previously said they were checking whether any passengers or crew had personal or psychological problems that might offer clues to why the plane vanished, along with the possibility of a hijacking, sabotage or mechanical failure.

Speaking earlier Friday, acting Transport Minister Hishammuddin Hussein said the country had yet to determine what happened to the plane after it dropped off civilian radar and ceased communicating with the ground around 40 minutes into the flight to Beijing.

He said investigators were still trying to establish with certainty that military radar records of a blip moving west across the Malay Peninsula into the Strait of Malacca showed Malaysia Airlines flight 370.

"I will be the most happiest person if we can actually confirm that it is the MH370, then we can move all (search) assets from the South China Sea to the Strait of Malacca," he told reporters. Until then, he said, the international search effort would continue expanding east and west from the plane's last confirmed location.

The Malaysian official said it had now been established with a "more than 50 percent" degree of certainty that military radar had picked up the missing plane.

Scores of plane and aircraft from 12 countries are currently involved in the search, which currently reaches into the eastern stretches of the South China Sea and on the western side of the Malay Peninsula, northwest into the Andaman Sea and further into the India Ocean.

Investigators have not ruled out any possible cause for the plane's disappearance.

Fox News' Catherine Herridge, Justin Fishel and The Associated Press contributed to this report.