Suspicions that the missing Malaysia Airlines Boeing 777, which disappeared exactly one week ago, was deliberately directed off-course or hijacked by an expert were revived on Friday as it emerged that the aircraft had flown hundreds of kilometres west from its last known point of contact through air corridors routinely traversed by pilots.
"What we can say is we are looking at sabotage, with hijack still on the cards," a senior Malaysian police official told Reuters.
Citing military officials, the news agency said the aircraft had been tracked by military radars on a course far west of its last known contact.
Aviation experts The Hindu spoke to suggested the flight's course indicated it had been deliberately directed off-course and commandeered by someone who was an expert or veteran, either from the flight's crew or among the 239 people on board.
The last navigational way point - a geographic reference for pilots - tracked by Malaysian military radars, called IGREX, was south of the Andaman Islands. The Boeing 777 charted a careful, zig-zag course to IGREX from the point where it lost contact with air traffic control over the Gulf of Thailand.
That point, called IGARI, was reached by the Boeing at 1.21 am local time on Saturday, an hour after take-off from Kuala Lumpur. At that same time, the transponders of the aircraft stopped communicating with air traffic control, suggesting they may have been manually disconnected.
The Boeing, military officials said, then abruptly turned west to another well-known waypoint, VAMPI, northeast of Indonesia. It then turned north to the waypoint GIVAL, south of Phuket.
Curiously, the Boeing then sharply turned northwest to the waypoint IGREX, which is just south of the Andamans and along the route to Port Blair. That was the last point of tracking by Malaysian military officials.
How did the aircraft evade detection by Indian military radars on the Andamans? One possibility, seen as the most likely by many officials, is it could have crashed in the waters of the Andaman Sea or further west.
United States investigators said the plane flew for around four hours past its last point of contact at 1.21 am, citing intermittent "pings" from the aircraft to its satellite contact, which would have continued even if transponders had been disabled.
Captain Mohan Ranganathan, a former airline instructor and veteran pilot who flew frequently in the region, said there were at least two other possibilities.
Considering India's military installations in the Andamans, it is unlikely a Boeing 777 could have avoided detection. "It is possible a fictitious flight plan was obtained, from Medan (in Indonesia) to Male (in the Maldives) or beyond, so the aircraft would have clearance," he said, adding the aircraft could subsequently have diverted its course.
The plane had enough fuel, flying at 30,000 feet, to cross the Arabian Sea and even reach the western coast of Africa, he pointed out, and could have charted a course to avoid detection at Chennai or Thiruvananthapuram. The satellite link could also be deactivated, he said, as circuit breakers were in the cockpit. That leaves the likelihood the plane flew even beyond four hours.
Whether the Boeing crashed into the waters of the Indian Ocean, or charted a course elsewhere, its disappearance has been seen by aviation experts as among the most baffling mysteries of its kind.
But one thing they agree on is that the plane must have been commandeered by someone "who is an experienced pilot, and possibly had flown this route before", one veteran pilot said.
"It is somebody," added Captain Ranganathan, "who knows the aircraft like the back of his hand".