Despite a months-long, multi-million dollar search, the missing Malaysian Airlines flight MH370 and the 239 people on board remain lost.

Sunday marks a year since the Beijing-bound jet disappeared from radar over the South China Sea.

Hope for a miracle conclusion has long since faded, with the Malaysian government officially declaring the disaster an ‘accident’, with all passengers and crew presumed dead.

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The Australian-led search for the aircraft in the Indian Ocean continues, although Prime Minister Tony Abbott has hinted that its intensity may diminish as time goes on.

Nevertheless, in a speech to parliament on Thursday, Mr Abbott promised the families of the seven Australians lost on the flight that his government would continue working as best it could to resolve “one of the greatest mysteries of our time”.

Malaysian leader Najib Razak and Mr Abbott have collaborated on the ill-fated search for the missing plane.

Theories and conspiracies abound, led by Emirates president Sir Tim Clark, who has repeatedly alleged some form of international cover-up, pointing to numerous unanswered questions.

Here are some of the latest theories attempting to explain the aircraft’s disappearance, from the believable to the farfetched.

Leading theory: pilot suicide

MH370 was flown 500kms off course to Pulau Perak, the home island of captain Zaharie Ahmad Shah in the Malacca Strait, before being ditched into the sea, a new theory suggests.

The pilot made the diversion as an emotional farewell to his home, a senior pilot says, before flying repeatedly in and out of Malaysia and Thai airspace to confuse traffic controllers.

British captain Simon Hardy spent six months trawling through flight data to come to this conclusion.

In a recent book, former New Zealand airline boss Ewan Wilson claims that the captain locked his co-pilot out of the cockpit, turned off the plane’s oxygen supply, and then landed the plane on the water so it sank in one piece without breaking into debris.

If true, this would be the seventh case of pilot suicide, bringing the number of confirmed deaths caused deliberately by pilots to 900.

The US shot it down

The missing plane was blown up in mid-air by the US military because it feared the plane had been hijacked, former French airline boss Marc Dugain says.

The Island of Diego Garcia, where the United States has an army base.

It was shot down to protect the US army base on Diego Garcia island from a September 11-style attack, he says.

Nearby islanders saw the missing plane flying low close to the base the day it disappeared, claims the former CEO of now-defunct Proteus Airlines.

In previous interviews, CIA director John Brennan has not ruled out the possibility of a terrorist attack, but noted that no groups have claimed responsibility.

Fire in the cockpit

Former pilot Chris Goodfellow claims an electrical fire onboard MH370 explains the plane’s western turn and silent transmitting system.

The pilots were too busy trying to divert the plane and make an emergency landing on the island of Langkawi to make a distress call, Mr Goodfellow says.

MH370 pilots Zaharie Ahmad Shah (L) and Fariq Abdul Hamid (R). Photo: AAP

Smoke in the cockpit might then have incapacitated the pilots before they could land, with MH370 continuing above the Indian Ocean until it ran out of fuel and crashed, he says.

James Fallows from The Atlantic says Goodfellow’s explanation makes better sense than anything he’s heard so far.

Putin sent the plane to Kazakstan

Upset by sanctions imposed by the American government, Russian President Vladimir Putin ordered a hijacking of the plane to punish his enemies, redirecting the plane to Kazakstan.

That is the theory of pilot and science writer Jeff Wise, who claims hijackers interfered with the plane’s tracking equipment to throw investigators off the trail, before flying along an unmonitored route.

In a 4000-word article for New York Magazine, which has gone viral, Wise says the plane was then buried at an airport in Kazakhstan, which happened to have been bulldozed just before the disappearance.

The Independent Group, a group of scientists and engineers researching MH370, call Wise’s theory “a bunch of garbage”.

Taliban hijaked the plane

Another far-fetched theory is that the Taliban hijacked the plane in Pakistan – an idea with support from News Corp chief Rupert Murdoch and retired US air force Lieutenant General Thomas McInerney.

Mr McInerney believes the plane will be used against the US or its allies later for terrorism, and points to the fact that Israel beefed-up security in the days following MH370’s disappearance.

In a controversial tweet, Murdoch says the flight has been “stolen” and “hidden”, perhaps in Northern Pakistan.

A spokesperson for the Taliban told Reuters the theory is “wild” and that they did not have any information about the missing plane as it was an “external issue”.

World seems transfixed by 777 disappearance. Maybe no crash but stolen, effectively hidden, perhaps in Northern Pakistan, like Bin Laden.

— Rupert Murdoch (@rupertmurdoch) March 15, 2014