PERTH, Australia (AP) — Former Australian Prime Minister Tony Abbott has said the “top levels” of the Malaysian government long suspected that the disappearance of Malaysia Airlines Flight 370 almost six years ago was a mass murder-suicide by the pilot.

Abbott was prime minister when the plane carrying 239 people vanished on March 8, 2014, while flying from Kuala Lumpur to Beijing.

Australia, working on Malaysia's behalf, coordinated what became the largest search in aviation history, but it failed to find the plane before being ended in 2017.

Speaking in a Sky News documentary to air on Wednesday and Thursday, Abbott said 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,” said Abbott, who was Australia’s prime minster from 2013 to 2015.

“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.”

In response, Malaysia's former prime minister and police chief said there was no conclusive proof of pilot suicide.

Former Prime Minister Najib Razak told the Free Malaysia Today online news portal that a possible pilot suicide was never ruled out but it would be “unfair and legally irresponsible" to pin the blame on Zaharie as the black boxes had not been found.

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 that investigators had “explored every single lead and possibility" but found no conclusive answer to why the plane vanished.

A Malaysian-led independent investigation report released in 2018 said the plane's course was changed manually but did not name a suspect and raised the possibility of “intervention by a third party.” Investigators, however, said the cause of the disappearance couldn't be determined until the wreckage and the plane's black boxes are found.

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Malaysia's Ministry of Transport didn't immediately respond to Abbott's comments. Malaysia has had a change of government since the plane's disappearance, with current Prime Minister Mahathir Mohamad ousting Najib, whose party had ruled Malaysia since its independence in 1957.

The pilot's family has long denied he was suicidal. The 2018 investigative report said there was no evidence of abnormal behavior or stress in the two pilots and none of the passengers had pilot training.

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.

The Australian-led search scoured 120,000 square kilometers (46,000 square miles) of the southern Indian Ocean and cost 200 million Australian dollars ($150 million). A private hunt by Texas-based company Ocean Infinity later searched more than 96,000 square kilometers (37,000 square miles) of sea.

Debris that washed ashore in the western Indian Ocean has been confirmed as coming from the missing Boeing 777 and indicated a broad expanse of the ocean where the plane likely crashed after running out of fuel.

Australia, Malaysia and China agreed in 2016 that an official search would only resume if the three countries had credible evidence that identified a specific location for the wreckage. Most of the passengers were Chinese.

Abbott believed a new investigation was 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.

Abbott's comments reopened old wounds for some families.

Jacquita Gomes, whose husband Patrick was a flight attendant on the plane, said it was frustrating that Abbott revealed this six years late.

“Why now? If it's true, for six years, we have been living a lie," she said.