Few mysteries have inspired such heated debate as the disappearance of Malaysian airliner MH370, its 12 crew and 227 passengers.
Searchers scouring huge swathes of the world's oceans for the jet have so far found no sign of it and theories of what happened, from the credible to the downright crackpot, have continued to abound.
Here aviation and security experts examine the plethora of theories that have sprung up in the eleven months since the jet disappeared from radar on March 8, 2014 after apparently changing course three times.
Anthony Glees, an author and the director of the Centre for Security and Intelligence Studies at the University of Buckingham, and former British Airways pilot Alastair Rosenschein have given their opinion on each of the theories, based on their expert knowledge.
Did the pilot hijack his own plane?
Pilot Zaharie Ahmad Shah planned mass murder because of personal problems, locking his co-pilot out of the cockpit, closing down all communications, depressurising the main cabin and then disabling the aircraft so that it continued flying on auto-pilot until it ran out of fuel.
That was the popular theory in the weeks after the plane's disappearance.
His personal problems, rumours in Kuala Lumpur said, included a split with his wife Fizah Khan, and his fury that a relative, opposition leader Anwar Ibrahim, had been given a five-year jail sentence for sodomy shortly before he boarded the plane for the flight to Beijing.
But the pilot's wife angrily denied any personal problems and other family members and his friends said he was a devoted family man and loved his job.
This theory is also the conclusion of the first independent study into the disaster by the New Zealand-based air accident investigator, Ewan Wilson.
Wilson, the founder of Kiwi Airlines and a commercial pilot himself, arrived at the shocking conclusion after considering 'every conceivable alternative scenario'.
However, he has not been able to provide any conclusive evidence to support his theory.
The claims are made in the book 'Goodnight Malaysian 370', which Wilson co-wrote with the New Zealand broadsheet journalist, Geoff Taylor.
It's also been rumoured that Zaharie used a flight simulator at his home to plot a path to a remote island.
However, officials in Kuala Lumpur declared that Malysian police and the FBI's technical experts had found nothing to suggest he was planning to hijack the flight after closely examining his flight simulator.
Professor Glees said: 'Had a pilot wished to kill himself and his passengers, he had no need to do it in such a bizarre way, indeed he could have crashed the plane the moment the transponder was turned off. Without a shred of supporting evidence, this theory simply doesn't stack up.
'What's more, I was told by someone senior who knew both the airline and the pilot that the chief pilot was one of their best and would not have been allowed to fly if there had been any sign of health or mental issues.'
Mr Rosenschein said: 'This is a possibility. It is both plausible and fits all the known facts about the disappearance.
'But, it is not possible to claim the transponder was turned off as the Malaysian Transport Minister stated. All that could be said is that the signal ceased to be received from the transponder.
'This may seem like a subtle distance, however the Malaysian authorities by stating incorrectly that the transponder was turned off led everyone to believe this was a hijacking or a suicide for which there is not a shred of evidence.'
The co-pilot was the real hijacker
Co-pilot Fariq Abdul Hamid, 27, again for personal problems, was suspected by rumour-spreaders to have overpowered the pilot and disabled the aircraft, flying it to its doom with crew and passengers unable to get through the locked cockpit door.
Theorists have put forward the suggestion that he was having relationship problems and this was his dramatic way of committing suicide.
But he was engaged to be married to Captain Nadira Ramli, 26, a fellow pilot from another airline, and loved his job. There are no known reasons for him to have taken any fatal action.
Others have suggested that because he was known to have occasionally invited young women into the cockpit during a flight, he had done so this time and something had gone wrong.
Young Jonti Roos said in March that she spent an entire flight in 2011 in the cockpit being entertained by Hamid, who was smoking.
Interest in the co-pilot was renewed when it was revealed he was the last person to communicate from the cockpit after the communication system was cut off.
Professor Glees said: 'If you invite women into your cockpit, you are breaking bad but also proving you love life and the glamour of being a pilot at 35 thousand feet. You're not suicidal and you're not murderous.
'However, it is possible that those 'pretty girls' invited into the cockpit were Uighur separatists - the indigenous ethnic minority in China's Xinjiang region which are increasingly portrayed as auxiliaries of al-Qaeda - this is a theory I do quite like.'
Mr Rosenschein said: 'This too is possible although the cockpit door can be opened with determined effort from the cabin.'
Russians secretly landed MH370 at a space port in Kazakhstan
An expert has claimed the missing Malaysia Airlines flight 370 was hijacked on the orders of Vladimir Putin and secretly landed in Kazakhstan.
Jeff Wise, a U.S. science writer who spearheaded CNN's coverage of the Boeing 777-200E, has based his outlandish theory on pings that the plane gave off for seven hours after it went missing, that were recorded by British telecommunications company Inmarsat.
Wise believes that hijackers 'spoofed' the plane's navigation data to make it seem like it went in another direction, but flew it to the Baikonur Cosmodrome, which is leased from Kazakhstan by Russia.
However, Wise admits in New York Magazine that he does not know why Vladimir Putin would want to steal a plane full of people and that his idea is somewhat 'crazy'.
Wise also noted there were three Russian men onboard the flight, two of them Ukrainian passport holders.
Aviation disaster experts analysed satellite data and discovered - like the data recorded by Inmarsat - that the plane flew on for hours after losing contact.
Careful examination of the evidence has revealed that MH370 made three turns after the last radio call, first a turn to the left, then two more, taking the plane west, then south towards Antarctica.
Professor Glees said: 'What on earth would be the benefit to Putin of such a hijacking? Russia is a leaky country, and if this had happened, we'd certainly know by now.'
Mr Rosenschein said: 'Extremely unlikely. The aircraft would have been tracked on primary radar throughout the flight, quite apart from the implausible political scenario involving the Russian President.'
MH370 was used by terrorists for suicide attack on Chinese flotilla
This extraordinary claim came from 41-year-old British yachtsman Katherine Tee, from Liverpool, whose initial account of seeing what she thought was a burning plane in the night sky made headlines around the world.
On arrival in Thailand's Phuket after sailing across the Indian Ocean from Cochin, southern India with her husband, she said: 'I could see the outline of the plane - it looked longer than planes usually do.There was what appeared to be black smoke streaming from behind.'
Ms Tee's general description of the time and place was vague and she lost all credibility when she later stated on her blog that she believed MH370 was a kamikaze plane that was aimed at a flotilla of Chinese ships and it was shot down before it could smash into the vessels.
Without solid proof of the satellite data, she wrote on her blog, Saucy Sailoress, the plane she saw was flying at low altitude towards the military convoy she and her husband had seen on recent nights. She added that internet research showed a Chinese flotilla was in the area at the time.
Professor Glees said: 'Eye-witnesses are notoriously unreliable and if Ms Tee has the answer - the wreckage would have been found by now at sea.'
Mr Rosenschein said: 'Extremely unlikely and demonstrative of geopolitical naivety by Katherine Tee.'
The jet landed on water and was seen floating on Andaman Sea
On a flight from Jeddah to Kuala Lumpur that crossed over the Andaman Sea on March 8, Malaysian woman Raja Dalelah, 53, saw what she believed was a plane sitting on the water's surface.
She didn't know about the search that had been started for MH370. She alerted a stewardess who told her to go back to sleep.
'I was shocked to see what looked like the tail and wing of an aircraft on the water,' she said.
It was only when she told her friends on landing in Kuala Lumpur what she had seen that she learned of the missing jet. She had seen the object at about 2.30pm Malaysian time.
She said she had been able to identify several ships and islands before noticing the silver object that she said was a plane.
But her story was laughed off by pilots who said it would have been impossible to have seen part of an aircraft in the water from 35,000ft or seven miles.
Ms Raja filed an official report with police the same day and has kept to her story.
'I know what I saw,' she said.
Mr Rosenschein said: 'Aircraft are easily spotted flying high in the sky but are almost invisible on the surface when seen from the cabin of an aircraft at high cruising altitude.'
Professor Glees said: 'Eye-witnesses are always poor witnesses, alas, and especially so in aircraft disasters.
'They frequently say there was an explosion and then a crash when film evidence shows the crash comes first and then the explosion. They are not to blame. These things happen in a blink of the eye and are very traumatic.'
Major technical problem so pilots took evasive but doomed action
A catastrophic event such as a fire disabling much of the equipment resulted in the pilots turning the plane back towards the Malaysian peninsula in the hope of landing at the nearest airport.
Satellite data, believable or not, suggests the aircraft did make a turn and theorists say there would be no reason for the pilots to change course unless confronted with an emergency.
A fire in a similar Boeing 777 jet parked at Cairo airport in 2011 was found to have been caused by a problem with the first officer's oxygen mask supply tubing.
Stewarts Law, which has litigated in a series of recent air disasters, believes the plane crashed after a fire - similar to the blaze on the Cairo airport runway - broke out in the cockpit.
After an investigation into the Cairo blaze, Egypt's Aircraft Accident Investigation Central Directorate (EAAICD) released their final report which revealed that the fire originated near the first officer's oxygen mask supply tubing.
The cause of the fire could not be conclusively determined, but investigators pinpointed a problem with the cockpit hose used to provide oxygen for the crew in the event of decompression.
Following the 2011 fire, US aircraft owners were instructed to replace the system - it was estimated to cost US$2596 per aircraft. It was not known whether Malaysia Airlines had carried out the change.
If either pilot wanted to crash the plane, why turn it around? So the turn-around suggests they were trying to land as soon as possible because of an emergency.
Professor Glees said: 'The plane turned more than three times. Autopilots won't do this unless someone has set them to do this. Modern jets can suffer catastrophic failures which could include a shutdown of oxygen.
'If there had been an emergency, there was enough time to get a Mayday message out and the responder would not have been turned off deliberately.'
Mr Rosenschein said: 'This is plausible. Similar incidents have occurred previously and it is quite possible that this or a very similar technical fault explains the aircraft's disappearance.'
Lithium-ion batteries in the cargo hold exploded
MH370's cargo included a consignment of highly-inflammable lithium-ion batteries. It has been suggested that these ignited, or exploded due to a fire already present, perhaps caused by a tyre bursting into flames on take-off.
Pilot Chris Goodfellow posted on the internet that it was possible a poorly-inflated tyre caused a fire in the front landing gear during take off, which has happened in the past.
The smoke would have incapacitated the pilots, leaving the aircraft to cruise on autopilot until it ran out of fuel. A fire fits in with oil rig worker Mike McKay's sighting of what he believes was a plane on fire.
Lithium-ion batteries - which are used in mobile phones and laptops - have been responsible for a number of fires on planes and have even brought aircraft down in recent years.
According to US-based Federal Aviation Administration, lithium-ion batteries carried in the cargo or baggage have been responsible for more than 140 incidents between March 1991 and February 17 this year, it was reported by Malaysiakini.
In one case, UPS Airlines Flight 6 crashed while attempting an emergency landing in September 2010 en route from Dubai to Cologne in Germany.
The MH370 cargo also included mystery items not declared in the manifest, but which were later described by Malaysia Airlines officials as 'radio parts'.
There was a weight discrepancy in the goods listed on the manifest and it was only under pressure from questioners that the airline spoke of radio parts, but doubts about the entire cargo remain.
The mystery remains as to whether those 'radio parts' caused an explosion.
Mr Rosenschein said: 'Whilst lithium-ion batteries are flammable and can cause severe damage to an aircraft, the tyre burst scenario would have been known to the crew on takeoff and they would not have continue their climb without instigating the standard emergency landing gear fire drill.'
Professor Glees said: 'Had the plane come down because of an explosion it would not have executed turns and flown on, and the transponder would not have been turned off.
'Had MH370 exploded, wreckage would have been found long ago.'
Shot down by the U.S. who feared terror attack on Diego Garcia
The Boeing 777 was shot down by the Americans who feared the aircraft had been hijacked and was about to be used to attack the U.S. military base on Diego Garcia atoll in the Indian Ocean. So conspiracy theorists claim.
And former French airline director Marc Dugain said he had been warned by British intelligence that he was taking risks by investigating this angle.
There is no way of checking whether Dugain received such a warning or why he believes the Americans shot down the plane.
But adding to the theory that the aircraft was flown to Diego Garcia, either by the pilot Zaharie or a hijacker, was the claim that on the pilot's home flight simulator was a 'practice' flight to the island.
Professor Glees said: 'The Americans would have no interest in doing anything of the kind and not telling the world.
'In theory, they might wish to shoot down a plane they thought was attacking them but they wouldn't just fire missiles, they'd investigate it first with fighters and would quickly realise that even if it had to be shot down, the world would need to know.'
Mr Rosenschein said: 'The U.S. would not have been able to hide this fact and in any event, if it were true, they would have admitted their action as it would have prevented a successful terrorist action on this occasion and acted as a deterrent for future terrorist attacks.'
MH370 and its passengers have been kidnapped by aliens
Aliens abducted the plane - or so five per cent of Americans surveyed by Reason.com believe.
There were a number of recent UFO sightings in Malaysia around the time of the aircraft's disappearance, it was claimed, and one of these 'lifted it away'.
Alexandra Bruce, of Forbidden Knowledge TV, said that aliens had to be involved, based on footage she has seen of something that could only be termed 'a UFO' and on her own analysis of radar data.
Added to the alien theory was a comment by a UFO blogger who said that Malaysia's air force chief, Rodzali Daud, had confirmed that military radar had detected a UFO in an area in the northern Malacca Strait at 2.15am local time about an hour after the plane vanished.
Professor Glees said: 'Next they'll say Elvis was flying the plane.'
Mr Rosenschein said: 'Most Americans are religious and therefore can hold mystic beliefs. Total nonsense.'
It was an insurance scam
The plane was hijacked and brought down by a passenger or a crew member playing an insurance scam so that he or she would die and relatives would benefit from compensation - a suggestion put forward in the early days by none other than Malaysia's Inspector General of Police, Khalid Abu Bakar.
'We are looking at all possibilities,' he told a packed press conference in Kuala Lumpur.
'We are studying the behavioural pattern of all the passengers.'
This, he said, included a passenger who might owe a lot of money to someone.
The police investigations into what caused the plane's fate included questioning workers at an orchard where mangosteens are grown.
This was in case explosives had been planted in a consignment of the fruit that had been loaded onto the aircraft.
Professor Glees said: 'This was a case of mass murder. Insurance scams are in a completely different order of magnitude. And there are the three turns...'
Mr Rosenschein said: 'This is more likely to have been committed by one or other of the pilots rather than by a passenger. Unlikely though this might be, it is none the less it is plausible.
Espionage between China and the U.S.
Internet writer 'Dark Spectre' has put forward a theory on Reddit.com that the presence on the aircraft of 20 employees of Freescale Semiconductor - a company which manufactures sophisticated surveillance technology - could be the reason for the plane disappearing.
Dark Spectre said China could have been determined to capture a group of private contractors who helped the National Security Agency to conduct spy operations against Beijing.
Referring to the apparent deaths of all on board, he asked what would 200 lives be to the Chinese for the chance of find out the scope of the US's intrusion?
The problem with his theory is that the plane was flying to Beijing anyway, so why try some complex kidnapping?
Professor Glees said: 'So where is the plane? If this theory were correct, the plane wouldn't have disappeared.'
Mr Rosenschein said: 'It is highly unlikely that either China or the US would commit mass murder in such a public way for so little advantage.
'In any event, it would not explain the aircraft being re-routed.'
Mossad was to blame
The Israeli secret service did it, according to another suggestion doing the rounds of the internet.
Conspiracy theorists, who often blame Mossad for most mysteries, say Israeli agents planned to carry out a 9/11-style attack on Kuala Lumpur's tallest building, the Petronas Twin Towers, and blame it on Iran.
There were, conspiracy believers point out, two Iranian nationals travelling on false passports among the passengers.
However, it transpired that the men had bought the stolen passports to travel to Europe to start new lives in Germany and Denmark.
Niloufar Vaezi Tehrani, the mother of one of the men, Pouria Nourmohammadi, confirmed she had been waiting for him to arrive at Frankfurt airport after he was due to change flights in Beijing.
If MH370 had been commandeered to be crashed, why wasn't it flown into the towers?
Professor Glees said: 'What on earth would be the advantage to Mossad of hijacking the plane? And if Mossad had hijacked it, they would not then have destroyed it without trace. What would be the point of that? If Mossad do a thing, they do it right.'
Mr Rosenschein said: 'Anti-Semites will blame everything and anything on the Jews. Utter nonsense. This scenario is to be treated with the contempt it deserves.'
MH370 was flown to a remote hangar to be used by terrorists
Despite the hopes of relatives of MH370 passengers that their loved ones are still alive after being caught up in a plot to hijack the aircraft and hide it in a remote hangar - to be used at a later date for an evil purpose - this scenario appears too far-fetched to be believed.
The 'hideouts' include a remote area of north west Australia over which no other aircraft fly, disused wartime air strips on islands and one of the former Soviet satellite nations.
Aside from a hijacking team being able to hold 239 passengers and crew hostage for almost a year without a scrap of evidence to suggest that this had happened is the question why the plane hasn't been put into operation for a wicked plot by now.
Following on from remote hangar conspiracy theory is the claim in Russian newspaper, Moskovsky Komsomolets, that it had been told by a military source that the plane is in Afghanistan after being hijacked by terrorists, the leader being a person called Hitch.
The passengers, it is claimed, have been divided into seven groups and are living in mud huts near the border with Pakistan.
But to have reached Afghanistan, MH370 would have had to fly through the airspace of several countries and it would have been picked up by their radar because it would have broken away from regular, plotted air routes.
Professor Glees said: 'Not implausible, not to be rejected out of hand. But if the purpose was to hijack the plane and use the hostages to barter with some government, something must have happened to have put a spoke in the wheel.'
Mr Rosenschein said: 'It could be done but would be impossible to do so in total secret.'
Hijacked and shot down over Ukraine to discredit Russia
MH370 was destroyed when it was shot down over Ukraine, in a devious plot by the Americans.
Several websites have claimed that after hijacking MH370, a CIA team flew it to Holland and then used it under the flight number MH17 to fly over Ukraine where it was deliberated crashed by US agents to discredit Russia.
MH17 flying from Amsterdam to Kuala Lumpur was travelling over the conflict-hit region when it disappeared from radar.
A total of 283 passengers, including 80 children, and 15 crew members were killed.
If such a bizarre plot was even discussed, why would the Americans hijack a plane then fly it to Holland, before deliberately crashing it - when all they had to do was hijack the real MH17?
A second 'swap' theory debated in The Conversation website says the biggest conspiracy claims that after being hijacked, MH370 was flown somewhere secret, stored for a while, then it was rigged with explosives before being flown over Donestsk and blown up in order to implicate one of the parties.
No explanation appears to have been given for the passengers who had booked on the real MH17.
Professor Glees said: 'This comes from the tooth fairy's book of make-believe.
'We knew within minutes of the shooting down of MH17. MH370 was nowhere near Ukraine and could not have got anywhere near without every government knowing.'
Mr Rosenschein said: 'Complete and utter nonsense. It would have required the collusion of Malaysia Air, it's staff and crew, not to mention hundreds of passengers.'
The CIA know, says Malaysia's former Prime Minister
Malaysia's former Prime Minister, Mahathir Mohamad claimed on his blog that there has been a cover up and the CIA and Malaysia know exactly what happened to the plane.
'Airplanes don't just disappear. Certainly not these days with all the powerful communication systems, radio and satellite tracking and film-less cameras which operate almost indefinitely and possess huge storage capacities,' he wrote.
Dr Mahathir, 88, who was Malaysia's prime minister between 1981 and 2003, said the missing flight's communication system 'must have been disabled'.
'Or else the flight of MH370 would have been tracked by satellites which normally provide data on all commercial flights, inclusive of data on location, kind of aircraft, flight number, departure airport and destination.
'But the data seems unavailable. The plane just disappeared seemingly from all screens.'
It is questionable that a modern aircraft could vanish without a trace, apparently baffling the world's scientists, analysts and all manner of aviation experts.
Is Dr Mahathir right? Does a government, a government agency, a military force, know something?
Mr Rosenschein said: 'Malaysia's former Prime Minister has been reading too many conspiracy books. Political nonsense.'
Professor Glees said: 'Clearly someone somewhere knew something at some stage. But that someone may now be dead or not talking.'
The plane was brought down by remote control
It was a high-tech plot, say the conspiracy theorists.
The plane crashed by remote control with someone accessing the jet's computer and reprogramming everything, causing it to go down.
However, the woman who came up with the theory - Dr Sally Leivesley, a former British Home Office official - was revealed as running her own company which trains businesses and governments to defend themselves against terrorist attacks.
And how was anyone going to target the computer of that particular aircraft - and why?
Professor Glees said: 'Sally is a really smart lady whose views are widely respected. But why would anyone want to bring the plane down and then keep it a secret?
'Bringing it down would have been done for a purpose. What would such a purpose be, and how would bringing a plane down serve it? What would be the point of destroying a plane and then saying nothing about the reason for its destruction?'
Mr Rosenschein said: 'Another nonsense theory by someone with no technical knowledge of modern civil aircraft.
'Dr Leivesley has jumped onto this bandwagon with scant regard for the facts. Implausible.'
MH370 'hid' from radar by shadowing a Singapore Airlines flight
MH370 flew in the 'shadow' of another jet - a Singapore Airlines flight - through Indian and Afghanistan airspace, using that aircraft as a shield to avoid radar.
It could have done this successfully, said blogger Keith Ledgerwood, because its own transponder was switched off.
To have succeeded in doing this, and for whatever reason, the two planes would have had to be within 3,300ft of one another and being that close, the Singapore Airlines crew would have known about the other aircraft and reported it.
Professor Glees said: 'This theory relies on there having been conspiracy and collusion. But no evidence of either has been presented and it would not be easy to hide either, indeed easy to uncover both.'
Mr Rosenschein said: 'This is possible but highly unlikely to be done without detection.'
The experts' verdicts
Professor Anthony Glees: Politically motivated hijack
'At the time, and for many weeks after the disappearance of MH370, I thought the evidence pointed towards a hijack with a political motive,' he explained.
'Bearing the destination of the plane in mind, my thinking was that this was a Uighur plot and that the plane was flown to some Islamic state or, if the hijackers were planning another 9/11 but on Beijing, the plane was probably shot down somewhere over China.
'We know that on the one hand the Uighurs had Islamist terrorists among their numbers, that they liked attacking transport centres and could use primitive but effective weapons. On the other we know that the Chinese security forces believe that the best way of dealing with Uighur Islamists is to try to disrupt them whilst preventing any news of their measures from creeping out.'
Alastair Rosenschein, former BA 747 pilot: Technical malfunction
'My personal belief is that a technical malfunction resulted in a depressurisation followed by a hypoxia event causing the flight crew to pass out,' he said.
'The aircraft flew on until it ran out of fuel and crashed in the Southern Indian Ocean.'
- Daily Mail