UPDATE: The mysterious disappearance of Malaysia Airlines MH370 took an even more intriguing turn on Saturday, March 15, when Malaysian Prime Minister Najib Razak said "deliberate action" by someone on the plane was behind what happened. It has been confirmed that the plane - which departed at 12.40am on March 8 - had its Aircraft Communications Addressing and Reporting System (Acars) disabled less than an hour later. Its transponder was then switched off, and the plane turned back. It was spotted north-west of Penang at 2.15am. Intriguingly, it was again spotted at 8.11am by a satellite.
Who on board had such aviation knowledge to do all that?
On Saturday, Malaysian police searched the home of Captain Zaharie Ahmad Shah, 53. They arrived at 2.40pm and left at around 4:45pm.
It was reported that investigations will include political and religious leanings, and the travel pattern of the captain and his co-pilot Fariq Abdul Hamid, 27. The probe will also include their hobbies and behaviour with their friends.
Below are some of the other popular theories so far.
1. The plane travelled on for several hours
The Wall Street Journal suggested in a report on Thursday that the Malaysia Airlines flight had flown on for about four hours after its last reported position, which would mean that it travelled on for hundreds of miles.
The theory was promptly debunked later that day by Malaysia's Acting Transport Minister Hishammuddin Hussein, who called the report "inaccurate" during his press conference. Rolls-Royce, which supplied the Trent engines for the Boeing 777, said on Friday it concurred with what the Malaysia government said.
However, this theory seems to have gained new momentum as the White House officially got in the act with a press conference. White House spokesman Jay Carney said: "It's my understanding that based on some new information that's not necessarily conclusive, but new information, an additional search area may be opened in the Indian Ocean."
This tallied with previous US media reports that the Malaysia Airlines Boeing 777's communication system continued to "ping" a satellite for a number of hours after it disappeared off radar.
It also dovetails with an early report on Sunday which said the plane may have turned back from its scheduled route to Beijing before disappearing.
2. Pilot fault
With little information emerging over the past week about the flight, attention has turned to the pilots, especially since a young South African woman came forward to tell Australian television that MH370's First Officer Fariq Abdul Hamid (in the picture above), 27, allowed her and a friend into the cockpit of a plane he was co-piloting in 2011, flouting official rules.
Authorities were also investigating MH370's pilot, Captain Zaharie Ahmad Shah (below), 53, as well as all 227 passengers on board.
However, friends and colleagues have come forward to defend both men as professionals and Malaysia Airlines declined to reveal more details about the duo.
3. MH370 caught fire over South China Sea
Mr Mike McKay, a New Zealand oil rig worker, came forward to say he saw the missing flight MH370 on fire around the time of its disappearance.
He said he saw "the plane burning at high altitude... in one piece" about 50 to 70km from the Songa Mercur drilling platform in the South China Sea.
While Vietnamese officials confirmed that they had received the letter he e-mailed, they said they found no wreckage at the coordinates he pinpointed.
4. Plane had 'structural issue'
Stanford computer science student Andrew Aude put forward a theory, which went viral on the Web on Wednesday, that the plane had a structural issue.
Based on a Federal Aviation Authority directive which pointed to the fuselage cracking at a spot where the satellite antennae is located, Mr Aude's theory could accommodate both the knocking out of the plane's communications systems as well as the possibility that the passengers and crew were turned unconscious by a slow decompression of the plane.
"If the decompression was slow enough, it's possible the pilots did not realise to put on oxygen masks until it was too late," he wrote.
The theory that the flight might have been hijacked got a boost with the revelation on Friday that communications with the plane could have been deliberately turned off.
According to US media, the aircraft's data reporting system and its transponder - which reports its position in flight to ground-based radar - were shut down separately at a 14-minute interval. This, according to an ABC new report, suggests that they may have been deliberately disabled or at any rate did not fail as a result of a catastrophic airframe incident.
A Washington Post report also added that the transponder was switched off 30 minutes after the final voice communication from the cockpit, around the same time that Malaysia believes the plane may have inexplicably started to turn back.
These clues indicate that someone might have taken over control of the airplane.
6. Terrorist attack
This theory gained ground when it was revealed on Tuesday that two men who had boarded the plane with fake credentials from stolen passports were Iranian.
Mr Pouria Nour Mohammad Mehrdad (left), 19, had travelled on an Austrian passport, and Mr Delavar Seyed Mohammadreza (right), 29, on an Italian passport. Mr Pouria was identified by the Malaysian authorities after his mother told police he did not arrive in Frankfurt. But subsequent investigations into the duo's background have led the authorities to believe that the duo were illegal immigrants rather than terrorists.