BANGKOK // Thailand's military detected a plane that may have been Malaysia Airlines Flight 370 just minutes after the airliner's communications went down but did not share the information with Malaysia earlier because it was not specifically asked for it.
Radar picked up a twisting flight path that took the plane to the Strait of Malacca, Thai air force spokesman Air Vice Marshal Montol Suchookorn said on Tuesday. Malaysian radar also tracked Flight 370 to the same location early on March 8.
Thailand's failure to quickly share possible information regarding the fate of the plane with 239 people on board may not substantially change what Malaysian officials know, but it raises questions about the degree to which some countries are sharing their defence information, even in the name of an urgent aviation mystery.
With only its own radar to go on, it took Malaysia a week to confirm that Flight 370 had entered the strait, an important detail that led it to change its search strategy.
When asked why it took so long to release the information, Air Vice Marshal Montol said: "Because we did not pay any attention to it. The Royal Thai Air Force only looks after any threats against our country, so anything that did not look like a threat to us, we simply look at it without taking actions."
He said the plane never entered Thai airspace and that Malaysia's initial request for information in the early days of the search was not specific.
Flight 370 took off from Kuala Lumpur at 12.40am Malaysian time and its transponder, which allows air-traffic controllers to identify and track the airplane, ceased communicating at 1.20am.
Air Vice Marshal Montol said that at 1.28am, Thai military radar "was able to detect a signal, which was not a normal signal, of a plane flying in the direction opposite from the MH370 plane", back towards Kuala Lumpur. The plane later turned right, toward Butterworth, a Malaysian city along the Strait of Malacca.
He said he did not know exactly when Thai radar last detected the plane. Malaysian officials have said Flight 370 was last detected by their own military radar at 2.14am
The search area for the plane initially focused on the South China Sea, where ships and planes spent a week searching. Pings that a satellite detected from the plane hours after its communications went down have led authorities to concentrate instead on two vast arcs - one into central Asia and the other into the Indian Ocean - that together cover an expanse as big as Australia.
The Thai information came as China announced that intelligence checks on 153 Chinese passengers aboard the airliner had produced no red flags.
Two thirds of those on board were Chinese, and Malaysia had asked authorities in Beijing to run an exhaustive background check on all their nationals as part of a probe into everyone aboard.
Lending fresh weight to the belief that the plane was deliberately diverted, the New York Times reported that the first turn it made off its flight path was programmed into the Boeing 777's computer navigation system, probably by someone in the cockpit.
Rather than manually operating the plane's controls, whoever altered Flight 370's path typed seven or eight keystrokes into a computer situated between the captain and the co-pilot, the newspaper said, quoting US officials.
The head of Malaysia Airlines, Ahmad Jauhari Yahya, said he was unable to confirm the report.
Malaysian officials insist they are investigating all the passengers and crew, but for the moment the focus is clearly on the two pilots - Captain Zaharie Ahmad Shah and First Officer Fariq Abdul Hamid.
On Monday Mr Ahmad Jauhari revealed that the last recorded words from the cockpit - "All right, good night" - were almost certainly spoken by the co-pilot, Fariq.
The identity was deemed important given that the final message came around the time the plane's two automated signalling systems were disabled and it veered off course just as it was being handed over from Malaysian to Vietnamese air traffic control.
Despite some confusion about when the systems were switched off, the Malaysian transport minister Hishammuddin Hussein stressed that investigators still believe the series of events were consistent with "deliberate action" by someone on the plane.
*Associated Press and Agence France-Presse