As the search for the missing Malaysia Airlines plane enters a third week, there is no shortage of theories about its disappearance.
An in-flight fire, or a rapid fall in cabin pressure that knocked everyone out? Perhaps.
A major mechanical failure that shut all systems? Possible.
The plane turned away from its original flight path to attempt an emergency landing in Langkawi, just off the Malaysian island? Worth exploring.
With a massive multinational search now on in the southern Indian Ocean to locate debris that could belong to the missing aircraft, current thinking suggests an ill-intentioned takeover is unlikely. Why would a hijacker or terrorist take the plane to one of the remotest parts of the world?
Even so, aviation experts and seasoned pilots told The Sunday Times they still believe MH370 may have been hijacked - but not necessarily for ransom or other demands.
"It's possible there was something or someone on the plane that was important enough for an organisation or group to stage this," said a pilot with more than 25 years' experience, who asked not to be named.
Journalists have repeatedly asked for the cargo manifest to be released but all that the airline has said is that there were several tonnes of mangosteens, and lithium ion batteries that were certified safe for flight.
Mr Paul Yap, who heads Temasek Polytechnic's aviation school, said that two weeks after the plane vanished en route to Beijing from Kuala Lumpur, the signs still point to a deliberate takeover of the plane.
Authorities believe the plane's communication and tracking systems - the transponder, and the Aircraft Communications Addressing and Reporting System (ACARS) - were deliberately turned off.
That this happened just as the flight was leaving Malaysian air space and entering Vietnamese air space raises a red flag.
"When a handover happens, there is some sort of a radar 'black hole'. Nobody is really watching. In this particular area, the communications are also a little patchy and sometimes we have to call a few times to make contact," said another pilot who has been flying for 30 years.
Someone in the know would be aware that that would be the best time to take over an aircraft and chart a new course, he added.
According to Mr Yap, the erratic movements the plane made after air traffic controllers lost contact with the Boeing 777-200ER do not seem consistent with a mechanical fault or some other in-flight catastrophe.
The person or persons responsible were probably trying to escape radar detection, he said.
Even with the transponder off, scientific analysis of radar data has been able to verify, with some certainty, that the plane went up to 45,000 feet - much higher than the usual cruising altitude of about 35,000-37,000 feet - before descending to about 23,000 feet.
At one point, it was flying at about 29,500 feet.
Said an air traffic control expert: "Planes typically fly below or above this altitude. The traffic is usually divided so that aircraft going one way stay out of the way of planes going the other way. In between, at about 29,500 ft, there is a standby corridor.
"If the plane took this altitude and its communication systems were off, it could be to prevent a collision in the air."
Many pilots do not buy the in-flight fire and land-in-Langkawi theories either, because there was no distress call from the cockpit.
Even if there is total engine failure at 35,000 feet, a plane can continue to glide and pilots have about 15 to 20 minutes to do what they need to and send alerts.
In 1998, Swissair Flight 111 crashed into the Atlantic Ocean after smoke filled the cockpit and cabin. But not before the pilots reported the emergency.
Seven years later, Greek carrier Helios Airways crashed into a mountain when a lack of oxygen incapacitated the crew. Again, the pilots had time to send out a distress signal.
Said a 30-year veteran pilot: "Unless the plane broke up mid-air or there was an explosion, and both theories seem to have been ruled out, there is really no reason why the pilots could not call in an emergency unless they did not want to or were prevented from doing so."
The world is now waiting to find out if the debris located in the southern Indian Ocean belongs to MH370, said Mr Michael Daniel, a retired United States Federal Aviation Administration official.
"But even if it is from the missing aircraft, it is not enough evidence to rule out hijack or any of the possibilities that have surfaced," he said.