The captain of the missing Malaysia Airlines Flight 370 was a “lonely and sad” man who may have intentionally reduced oxygen in the cabin, “gently” killing passengers onboard before crashing the plane, a new report suggests.

The disturbing findings by a respected analyst probing the disappearance cast a new light on the mystery surrounding the cause of the likely crash of the international passenger plane after it suddenly stopped transmitting signals to air traffic controllers on March 8, 2014 while flying from Kuala Lumpur to Beijing.

To this day, families of the 227 passengers onboard the Boeing 777 aircraft are still tormented by the pain of not knowing their loved ones’ fate.

The passengers were mostly Chinese and there were six Australians on board.

The rest were from Malaysia, Indonesia, India, France, the United States, Iran, Ukraine, Canada, New Zealand, the Netherlands, Russia and Taiwan.

Family members of passengers onboard missing flight MH370 are still demanding answers. Photo: Getty

The 10 flight attendants onboard were all Malaysian, as was the co-pilot in training 27-year-old Fariq Hamid, and the pilot in command, Zaharie Ahmad Shah, 53.

The sudden disappearance of MH370 has perplexed millions of people around the world and prompted a series of costly international investigations to no avail.

Most agencies agree the aircraft crashed in the far southern Indian Ocean, several hours after deviating from its planned route about 40 minutes after take-off.

The flight is believed to have sharply diverted on a westward path across Malaysia, rather than north to its final destination of Beijing, before losing contact over the Andaman Sea.

Chunks of debris belonging to the aircraft have been found washed up on the French island of Reunion, and on the shores of Madagascar on the west coast of Africa.

Blaine Gibson, who is on a self-funded mission to find missing flight #MH370, finds new debris on Madagascar beach pic.twitter.com/EUJNaTc3vk

— CGTN (@CGTNOfficial) June 10, 2016

Search parties combed the beaches of Western Australia but did not find anything.

Last year’s safety report, produced by an international team, revealed the aircraft was likely steered off course on purpose and flown for several hours after communications were cut.

The route that most analysts believe MH370 followed before it disappeared.

Countless theories have circulated since the plane’s disappearance, ranging from plausible explanations to the downright absurd.

The latest explanation is a particularly disturbing one.

In the July issue of The Atlantic, respected writer and aviation specialist William Langewiesche revealed new findings that suggested captain Zaharie Ahmad Shah, known as Zaharie, had crashed the plane on purpose.

In his detailed report, Mr Langewiesche suggests Zaharie intentionally depressurised the cabin slowly so that “the effect would have gone unnoticed but for the sudden appearance of the drop-down oxygen masks”.

Whoever was in the cockpit, however, would have had access to four pressurised-oxygen masks with a supply that could last for hours.

“The cabin occupants would have become incapacitated within a couple of minutes, lost consciousness, and gently died without any choking or gasping for air,” Mr Langewiesche wrote.

“The scene would have been dimly lit by the emergency lights, with the dead belted into their seats, their faces nestled in the worthless oxygen masks dangling on tubes from the ceiling.”

While pilot suicides are rare, they do happen.

It is understood that Zaharie was experiencing a marriage breakdown at the time and was described by some who knew him as “often lonely and sad”.

His wife had moved out and was living in the family’s second house.

One of Zaharie’s friends, a fellow 777 captain, told Mr Langewiesche that he had reluctantly come to the conclusion that Zaharie was guilty.

Zaharie is believed to have suffered mental health issues before the disappearance of MH370. Photo: Facebook

“It’s hard to reconcile with the man I knew … but it’s the necessary conclusion,” the friend said.

“Zaharie’s marriage was bad. In the past he slept with some of the flight attendants.”

Mr Langewiesche claimed there was also a “strong suspicion among investigators in the aviation and intelligence communities that he was clinically depressed”.

Another notable finding that supports Mr Langewiesche’s view is a forensic examination of Zaharie’s flight simulator at home that revealed he experimented with a flight profile almost identical to the aircraft’s final doomed path, and that ended in fuel exhaustion over the Indian Ocean.

To this day, however, investigators have not yet reached a conclusion about what happened and the fate of passengers onboard MH370 remains a mystery.