Former Australian prime minister, Tony Abbott, believes MH370 was downed by one of its pilots in a murder-suicide.

Malaysia Airlines MH370 vanished while operating a scheduled service between Kuala Lumpur and Beijing on 8 March 2014. There were 239 people on board. Mr Abbott has told a Sky News documentary to be screened in Australia this week;

"My very clear understanding, from the very top levels of the Malaysian government, is that from very, very early on, they thought it was a murder-suicide by the pilot."

While plane's fate goes unanswered, theories abound

What happened to MH370 remains a mystery. Until the mystery is solved, various theories about the aircraft's fate abound.

Ean Higgins, a journalist at The Australian newspaper argues there are five main theories. First, a rogue pilot flying the aircraft until it ran out of fuel. Second, a hijack went awry. Third, an onboard fire. Fourth, a rapid decompression. Fifth, a lover's pact involving the Captain, his mistress, and a parachute.

There have been extensive searches for the remains of MH370. These searches have been focused on the eastern half of the Indian Ocean. Over 80,000 square miles of ocean and ocean floor have been searched.

Radar and satellite information points to MH370 flying a zigzag course over Malaysia and the Straits of Malacca before turning south into the Indian Ocean.  After biding Kuala Lumpur ATC goodnight, further radio contact ceased and the secondary radar transponder was turned off.

The lead agency on the first two-year search, the Australian Transport Safety Bureau (ATSB), has long held to the ghost flight theory. That is, the plane flew on unaided until it ran out of fuel.

Still looking for answers

Nearly six years after MH370 disappeared, plenty of people still agitate for answers. This week's Sky News documentary with input from a credible and informed ex-prime minister, promises to throw the spotlight back onto the missing plane.

Mr Abbott has told the documentary that the highest levels of the Malaysian government had briefed him. They believed veteran pilot, Captain Zaharie Ahmad Shah, deliberately downed MH370.

Mr Abbott's view contrasts with Malaysia's public position on the fate of MH370. Malaysian police chief and investigator Abdul Hamid Bado told Sky News there was no evidence of Captain Zaharie Ahmad Shah's involvement in the disappearance of MH370.

Malaysian transport minister Hishammuddin Hussein says there is no conclusive evidence either way.

Malaysian investigation cleared the Captain

A Malaysian government investigation found Zaharie Ahmad Shah to be a "well-adjusted" person and a very competent pilot. The investigation found no personal or financial problems that could have contributed to the Captain downing his own plane. In 2018, the chief investigator, Kok Soo Chon said;

"We are not of the opinion it could be an event committed by the pilot."

But another former prime minister, Malaysia's Najib Razak, says the murder-suicide theory was never ruled out and was investigated thoroughly.

Mr Abbott disputes the belief that Malaysia didn't want to lose face and admit one of its pilots was responsible for the disappearance of MH370. Mr Abbott said he had no reason to believe the Malaysian government was resistant to the murder-suicide theory because it might prove embarrassing.

Mr Abbott calls for the search to continue

While the fate of MH370 goes unanswered, Mr Abbott used the Sky documentary to make a call for the searching to continue.

"I'm not just referring to Australia here, I'm referring to all of the countries who had citizens on the plane. This is not something that a decent people can let go."

The families and friends of the 239 onboard would probably agree with that.