Twenty-one days after it disappeared en route from Kuala Lumpur to Beijing, there are still few facts that point to what exactly happened to Flight MH370.
Based on these, experts have three theories, though there may be more as clues emerge.
It is known that the jet's communication and tracking systems - the transponder, and the Aircraft Communications Addressing and Reporting System or ACARS - were turned off deliberately.
This happened as the Boeing 777-200ER was leaving Malaysian airspace and entering Vietnamese territory. Shortly after, it diverted from its original flight path.
The last satellite transmission was at 8.11am on March 8 - 6½ hours after Malaysian air traffic control lost contact with the jet. Until that point, there was no distress signal from the cockpit.
On Monday night, Malaysian Prime Minister Najib Razak confirmed, based on analysis of satellite data, that the plane had plunged into the Indian Ocean with zero chance of survivors.
No debris has been found.
The development ruled out several theories about MH370's disappearance and the fate of the 239 who were on board.
A major catastrophic mechanical failure is out. This would have caused a mid-air explosion which would have been detected.
A rapid fall in cabin pressure or in-flight fire is unlikely.
Even if there is a total engine failure at 35,000ft, a plane can continue to glide and pilots have about 15 to 20 minutes to do what they need to, such as 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, a Helios Airways plane crashed into a mountain when a lack of oxygen incapacitated the crew. Again, the Greek carrier's pilots had time to send out a distress signal.
After eliminating all implausible theories, experts are now left with three theories that match the passage of events with MH370.
It was a botched hijack where someone on the plane, or a pilot, took control but did not achieve his intention.
Such an incident occurred in 1996 when the captain of Ethiopian Airlines Flight 961 tried in vain to stop three hijackers seeking asylum in Australia while en route from Addis Ababa to Nairobi.
The plane crash-landed in the Indian Ocean near the Comoros Islands when fuel ran out. Of the 175 passengers and crew on board, 125 died - including the hijackers.
Malaysian authorities have said they did not receive any demands over MH370, but it is possible they were in negotiations with hijackers. Some questioned if the authorities or those on board could have tried talking with the hijackers, but the plane might have run out of fuel and crashed before a decision was made.
It is also possible the pilots or crew tried to stop the criminals. A fight could have broken out and the plane crashed.