Intelligence checks on the 153 Chinese passengers aboard a missing Malaysian airliner produced no red flags, China said Tuesday, as investigators struggled to clarify events that led to the plane's dramatic disappearance.
Eleven days after contact was lost with Flight 370 and its 239 passengers and crew, there has been minimal progress in determining what transpired when the Boeing 777 was deliberately diverted off its flight path and where it might have gone.
Two thirds of those on board were Chinese, and Malaysia had asked the authorities in Beijing to run an exhaustive background check on all their nationals.
Particular attention had been paid to one passenger from China's Muslim ethnic Uighur minority, separatist elements of which have become increasingly militant in their struggle against Chinese rule.
On Tuesday, China's ambassador to Malaysia Huang Huikang said no evidence had been found that would link anyone to a possible hijacking or terrorist attack on the jet, the official Xinhua news agency reported.
Huang also said China had begun searching for the aircraft in its own territory but gave no further details.
The potential search area, which was only properly identified after a week of fruitlessly scouring the South China Sea, is enormous -- stretching from the depths of the southern Indian Ocean, up and over the Himalaya and into central Asia.
China's state media has been vocally critical of Malaysia's handling of the missing plane investigation, saying valuable time and resources were wasted in the hours and days immediately after the aircraft disappeared on March 8.
On Monday, Premier Li Keqiang asked his Malaysian counterpart Najib Razak to provide more detailed information about the missing flight "in a timely, accurate and comprehensive manner".
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.
- A confusing timeline -
On Monday the head of Malaysia Airlines, Ahmad Jauhari Yahya, revealed that initial investigations indicated the last recorded words from the cockpit -- "All right, good night" -- were spoken by the co-pilot, Fariq.
Identifying the voice had been deemed crucial because officials initially said the words were spoken after one of the Boeing's two automated signalling systems -- Aircraft Communications Addressing and Reporting System (ACARS) -- had been manually disabled.
But Ahmad Jauhari contradicted that chronology, saying that the ACARS could have been switched off before or after Fariq spoke.
It could even have been disabled at the same time as the plane's transponder, which might possibly point back towards a general mechanical malfunction rather than human intervention.
The confusion is likely to fuel frustration with Malaysia's investigation, which has repeatedly stumbled in presenting contradictory information.
According to unidentified US officials cited by the New York Times on Tuesday, investigators believe the first turn the plane made away from its intended flight path was not effected manually but by a computer system that was most likely programmed by a person in the cockpit.
Use of the Flight Management System, which directs the plane from point to point according to the pre-submitted flight plan, would reinforce the theory that the plane was deliberately diverted by one of the pilots.
Twenty-six countries are now involved in searching for the jet after satellite and military radar data projected two dauntingly large corridors the plane might have flown through.
The northern corridor stretches in an arc over south and central Asia, while the other swoops deep into the southern Indian Ocean towards Australia.
At the far northern end of the arc, the central Asian states of Kyrgyzstan and Kazakhstan said there had been no sightings of the jet in their airspace.
Malaysia has deployed its navy and air force to the southern corridor, where Australia is taking the lead in scouring a vast section of ocean off its west coast.
-- An impossible search --
In a reflection of the enormity of the task, the US Pacific Fleet said it was withdrawing a guided missile destroyer from the search, because the area was simply too big for such a vessel to make an effective contribution.
Two long-range patrol aircraft -- a P-8A Poseidon and P-3C Orion -- would shoulder the main operational burden from now on, said Fleet spokesman Commander William Marks.
"The Indian Ocean goes so far, there probably aren't enough ships and aircraft in the world to search every inch of it," Marks told CNN.
"If you take a map of the United States ... it's kind of like saying, all right, I want to find a person somewhere between New York and California. I just don't know where they are," he said.
Malaysian police have searched both pilots' homes and are examining a flight simulator that Captain Zaharie, 53, had assembled at his home.
Associates say Zaharie was an active supporter of Malaysia's political opposition headed by veteran politician Anwar Ibrahim.
In a highly controversial case, Anwar was convicted of sodomy -- illegal in Muslim Malaysia -- just hours before MH370 took off.
Friends say Zaharie exhibited no extreme views, and Anwar said Tuesday he was "disgusted" by the suggestion that the captain may have sabotaged the plane as an act of political revenge.