KUALA LUMPUR:

An international land and sea search for a missing Malaysian jetliner is covering an area the size of Australia, authorities said on Tuesday, but police and intelligence agencies have yet to establish a clear motive to explain its disappearance.

Investigators are convinced that someone with deep knowledge of the Boeing 777-200ER and commercial navigation diverted Malaysia Airlines Flight MH370, carrying 12 crew and 227 mainly Chinese passengers, perhaps thousands of miles off its scheduled course from Kuala Lumpur to Beijing.

But intensive background checks of everyone aboard have so far failed to find anyone with a known political or criminal motive to hijack or deliberately crash the plane, Western security sources and Chinese authorities said.

Thailand’s military says its radar detected a plane that may have been from Flight 370 just minutes after the missing jetliner’s communications went down, and that it didn’t share the information earlier because it wasn’t specifically asked for it.

Thai air force spokesman Montol Suchookorn said Tuesday the plane followed a twisting flight path to the Strait of Malacca, which is where Malaysian radar tracked Flight 370 early March 8. But Montol said the Thai military wasn’t sure whether it detected the same plane.

Asked why it took so long to release the information, Montol said, “Because we did not pay any attention to it.” He said the plane never entered Thai airspace and that Malaysia’s initial request for information was not specific.

Malaysian Acting Transport Minister Hishammuddin Hussein told a news conference the Flight MH370 vanished from civilian air traffic control screens off Malaysia’s east coast less than an hour after take-off early on March 8.

Investigators piecing together patchy data from military radar and satellites believe that someone turned off the aircraft’s identifying transponder and ACARS system, which transmits maintenance data, and turned west, re-crossing the Malay Peninsula and following a commercial aviation route towards India.

Malaysian officials have backtracked on the exact sequence of events - they are now unsure whether the ACARS system was shut down before or after the last radio message was heard from the cockpit - but said that did not make a material difference.

“This does not change our belief, as stated, that up until the point at which it left military primary radar coverage, the aircraft’s movements were consistent with deliberate action by someone on the plane,” said Hishammuddin. “That remains the position of the investigating team.”

China’s ambassador to Malaysia said his country had carried out a detailed probe into its nationals aboard the flight and could rule out their involvement.

Malaysian police have searched the homes of the captain, Zaharie Ahmad Shah, 53, and first officer, Fariq Abdul Hamid, 27, both in middle-class suburbs of Kuala Lumpur close to the/sairport.

Among the items taken for examination was a flight simulator Zaharie had built in his home.

A senior police officer with direct knowledge of the investigation said the programs from the pilot’s simulator included Indian Ocean runways in the Maldives, Sri Lanka, Diego Garcia and southern India, although he added that US and European runways also featured.

“Generally these flight simulators show hundreds or even thousands of runways,” the officer said.

“What we are trying to see is what were the runways that were frequently used. We also need to see what routes the pilot had been assigned to before. This will take time, so people cannot jump the gun just yet.”

Malaysia has asked countries along both corridors, as well as others with satellite capabilities, to re-examine their data to try to narrow the search area, Hishammuddin said.

Meanwhile, Malaysian opposition leader Anwar Ibrahim condemned on Tuesday speculation that the captain of a missing Malaysian airliner - a member of his party and a distant relative - may have had political motives to sabotage the plane.

Describing Captain Zaharie Ahmad Shah as a “decent man”, Anwar said he was “disgusted” by what he saw as an attempt to smear the pilot and somehow implicate the opposition leadership in the March 8 disappearance of Malaysia Airlines Flight 370.

Hishammuddin blamed the speculation on foreign media reports and insisted that the search for the missing plane was “above politics.”