– A Malaysian investigation into the missing flight 370 has concluded that one or more people with flying experience switched off communications devices and deliberately steered the airliner off-course, a Malaysian government official involved in the investigation said Saturday.

The official called the disappearance a hijacking, though he said no motive has been established and no demands have been made known. It’s not yet clear where the plane ended up, said the official, who spoke on condition of anonymity because he was not authorized to brief the media.

The official said a deliberate takeover of the plane was no longer a theory. “It is conclusive,” he said, indicating that investigators were ruling out mechanical failure or pilot error in the disappearance.

He said evidence that led to the conclusion were signs that the plane’s communications were switched off deliberately, data about the flight path and indications the plane was steered in a way to avoid detection by radar.

Malaysian Prime Minister Najib Razak was scheduled to make a statement about the investigation on Saturday.

The Boeing 777’s communication with the ground was severed just under one hour into a Malaysia Airlines flight March 8 from Kuala Lumpur to Beijing. Malaysian officials previously have said radar data suggest it may have turned back toward and crossed over the Malaysian peninsula after setting out on a northeastern path toward the Chinese capital.

Earlier, an American official told the Associated Press that investigators are examining the possibility of “human intervention” in the plane’s disappearance, adding it may have been “an act of piracy.”

While other theories are still being examined, the U.S. official said key evidence suggesting human intervention is that contact with the Boeing 777’s transponder stopped about a dozen minutes before a messaging system on the jet quit. Such a gap would be unlikely in the case of an in-flight catastrophe.

The Malaysian official said only a skilled aviator could navigate the plane the way it was flown after its last confirmed location over the South China Sea. The official said it had been established with a “more than 50 percent” degree of certainty that military radar had picked up the missing plane after it dropped off civilian radar.

Why anyone would want to do this is unclear. Malaysian authorities and others will be urgently investigating the backgrounds of the two pilots and 10 crew members, as well the 227 passengers on board.

Some experts have said that pilot suicide may 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 in 1999.

A massive international search effort began initially in the South China Sea where the plane’s transponders stopped transmitting. It has since been expanded onto the other side of the Malay peninsula up into the Andaman Sea and into the Indian Ocean.

Scores of aircraft and ships from 12 countries are involved in the search.

The plane had enough fuel to fly for at least five hours after its last known location, meaning a vast swath of South and Southeast Asia would be within its reach. Investigators are analyzing radar and satellite data from around the region to try and pinpoint its final location, something that will be vital to hopes of finding the plane, and answering the mystery of what happened to it.

The USS Kidd arrived in the Strait of Malacca late Friday afternoon and will be searching in the Andaman Sea, and into the Bay of Bengal.

A P-8A Poseidon, the most advanced long range anti-submarine and anti-surface warfare aircraft in the world, will arrive Saturday and be sweeping the southern portion of the Bay of Bengal and the northern portion of the Indian Ocean.

Who were the pilots?

As speculation intensified that the missing plane might have been commandeered by someone with aviation skills, a picture began to emerge of the two pilots.

Police have said they are looking at their psychological background, their family life and connections as a line of inquiry into what happened to Flight MH370, which vanished early March 8 while en route from Kuala Lumpur to Beijing. There is no evidence linking them to any wrongdoing.

Pilots Zaharie Ahmad Shah and Fariq Abdul Hamid were described as respectable, community-minded men.

Fariq has drawn the greatest scrutiny after the revelation that in 2011, he and another pilot invited two women boarding their aircraft to sit in the cockpit for a flight from Phuket, Thailand, to Kuala Lumpur.

Malaysia Airlines said it was shocked by the report and was investigating.

Fariq, the son of a high-ranking civil servant in Selangor state, joined Malaysia Airlines in 2007. With 2,763 hours of flight experience, he had only recently started co-piloting the sophisticated Boeing 777.

Zaharie joined Malaysia Airlines in 1981 and had more than 18,000 hours of experience.

His Facebook page showed an aviation enthusiast who flew remote-controlled aircraft, posting pictures of his collection, which included a lightweight twin-engine helicopter and an amphibious aircraft.

Born in northern Penang state, the captain and grandfather was an enthusiastic handyman and proud home cook. As part of what he called “community service,” he had posted several YouTube videos including how to make air conditioners more efficient to cut electricity bills, how to waterproof window panes, and how to repair a refrigerator icemaker.