The "top levels" of the Malaysian government have long suspected that the disappearance of Malaysia Airlines Flight 370 nearly six years ago was an act of mass murder-suicide by the pilot, Australia's former prime minister said in an explosive interview that aired Wednesday.

The Boeing 777 carrying 239 people from Kuala Lumpur to Beijing vanished March 8, 2014, and is presumed to have crashed in the far southern Indian Ocean. A safety report into the disaster by an international team in July 2018 revealed the plane was likely steered off course deliberately by someone and flown for several hours after communications were severed.

Former Australian Prime Minister Tony Abbott, who was in office when the flight vanished, told Sky News Australia that high-ranking Malaysian officials believed veteran pilot Zaharie Ahmad Shah deliberately downed the jet.

“My very clear understanding, from the very top levels of the Malaysian government, is that from very, very early on they thought it was murder-suicide by the pilot,” Abbott told Sky News.

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Abbott, who was Australia's prime minister from 2013-15, made the comments in the first part of a Sky News Australia documentary "MH370: The Untold Story" that is airing Wednesday and Thursday.

“I'm not going to say who said what to whom, but let me reiterate, I want to be absolutely crystal clear, it was understood at the highest levels that this was almost certainly murder-suicide by the pilot, mass-murder-suicide by the pilot," Abbott said in the interview that aired Wednesday.

In the July 2019 issue of The Atlantic, writer and aviation specialist William Langewiesche delved into what happened to the missing aircraft, including a look at Shah, who had "indications of trouble." The night the aircraft went missing, control was seized in the cockpit during a 20-minute period between 1:01 a.m. and 1:21 a.m. and radar records show the autopilot was probably switched off, according to Langewiesche.

When the report by a 19-member international team was released in July 2019, chief investigator Kok Soo Chon said during a media briefing there was no evidence of abnormal behavior or stress among the two pilots – Capt. Zaharie Ahmad Shah and co-pilot Fariq Abdul Hamid – that could lead them to hijack the plane.

The report, however, did say the plane's course was changed manually but did not name a suspect and raised the possibility of “intervention by a third party.” Investigators stressed the cause of the disappearance still couldn't be determined until the wreckage and the plane's black boxes are found.

Langewiesche noted that while the co-pilot had nothing but a bright future ahead and no red flags in his past, Zaharie's life raised multiple concerns. After his wife moved out, the captain, who was reported to be "lonely and sad," also "spent a lot of time pacing empty rooms" and obsessed over two young internet models. The pilot's family, however, has long denied he was suicidal.

Forensic examinations of the pilot's simulator by the FBI also revealed he experimented with a flight profile that roughly matched what's believed to have happened to MH370, and that ended in "fuel exhaustion over the Indian Ocean." New York Magazine reported in 2016 that the simulated flight was conducted less than a month before the plane vanished.

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In his interview with Sky News, Abbott said he did not believe conspiracy theories centered on the Malaysian government, which owns Malaysia Airlines.

“I’ve read all these stories that the Malaysians allegedly didn’t want the murder-suicide theory pursued because they were embarrassed about one of their pilots doing this. I have no reason to accept that,” he said.

Scattered pieces of debris that washed ashore on African beaches and Indian Ocean islands indicate MH370 crashed in a distant stretch of the ocean, but a multi-government search by Australia, Malaysia and China has failed to pinpoint a location.

Abbott believes a new investigation is now warranted.

“Let's assume that it was murder-suicide by the pilot and if there is any part of that ocean that could have been reached on that basis that has not yet been explored, let's get out and explore it,” he said.

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Earlier this month, Malaysia said it has yet to decide on launching a new search due to not having received any new credible evidence to initiate one.

“However, the ministry will review any new evidence that it officially receives,” the Malaysian Ministry of Transport said in a brief statement to Reuters.

The comments came after Australia’s News Corp reported that a new search could be mounted, possibly this year, based on new evidence that it said showed the plane could have ended up in an area adjacent to the previous search area in the Indian Ocean. The U.S. exploration firm Ocean Infinity, which previously conducted a three-month search, was reportedly in discussions with the Malaysian government to launch a new search on a no-find, no-fee basis.

Ocean Infinity chief executive officer Oliver Plunkett said “no new search is imminent,” but the firm continues to engage with experts to identify where any new search might be launched.

“The Malaysian government, rightly in our view, set a high bar before they will engage in that discussion,” Plunkett told Reuters.

The Ministry of Transport has not yet commented about the remarks from the former Australian leader, according to The Associated Press.

Malaysian police chief Abdul Hamid Bador, who was one of the investigators, told local media that there was no evidence of Zaharie's involvement and that the plane's disappearance was still a mystery. Former Malaysian Transport Minister Hishammuddin Hussein said in a statement to the AP that investigators had “explored every single lead and possibility" but found no conclusive answer to why the plane vanished.

The Associated Press contributed to this report.