Mohammed Khairul Amri Selamat has come to the attention of police because of his alleged history as an aviation engineer at an executive jet charter company.  Police investigators believe someone with a background in aviation could likely have given Khairul the skills needed to operate the Boeing 777, although to what extent remains an open question.

"We are looking into Mohammed Khairul as well as the other passengers and crew,'' a police official with knowledge of the investigations said.

Malaysian authorities have also asked China to re-check the backgrounds of Chinese passengers on the flight for any suspicious links. "The manifests were forwarded to the Chinese authorities and it was cleared,  but I've asked Chinese intelligence and authorities to re-look, re-intensify, to the lists that they have with them,'' said Malaysian Transport Minister Hishammuddin Hussein.

China's ambassador to Kuala Lumpur later said China had ruled out foul play from the Chinese nationals aboard flight MH370.

In Malaysia, attention on Khairul comes amid reports that he had worked in Kuala Lumpur for Swiss jet charter company ExecuJet Aviation Group, which would have given him some aviation experience.

Khairul's family has denied any wrongdoing on his part.

According to Malaysian media, ExecuJet has refused to say whether Khairul is still employed with the company and the details of his career are not clear.  It's unclear exactly what type of engineer he is - which could have significant bearing on his ability to pilot a large commercial plane such as a 777.

Malaysian media has used the title "flight engineer'', which denotes a person who oversees the plane's systems in flight. But analysts say, with automation, the cockpit flight engineer position has largely been eliminated in modern aviation.

Stephen Fankhauser, aviation department head at Melbourne's Swinburne University, noted that on-board flight engineers were largely a thing of the past. Nonetheless, for anyone ''generically, there would be a lot of similarities'' between the operation of large and small jets.

But if Khairul was an aviation engineer who fixed planes, "It would take a great deal of deep learning'' in order for him to know his way around the 777 cockpit, said Brett Biddington, a Canberra-based aerospace expert.

The mystery of the flight has intensified since March 8 when the Malaysia Airlines Boeing 777 flying from Kuala Lumpur to Beijing lost contact with air traffic control an hour into the flight.

Once the plane went missing, Malaysian authorities considered the possibility of terrorism as the cause, with the focus turning initially to two Iranian passengers travelling on false passports. Authorities in Malaysia and elsewhere later said they were satisfied that the duo, Pouria Nour Mohammad Mehrdad, 19, and Delavar Seyedmohammaderza, 29, were likely migrants heading for Europe and not terrorists.

Since then, Malaysian authorities have claimed the transponder to the plane had been switched off and the plane flew for up to eight hours after it was no longer in contact with air traffic control. The path of the flight, originally thought to be over the the South China Sea, has instead been described as far over the Indian Ocean.

Scrutiny of Khairul has prompted his father, Omar, to defend his son's reputation, telling The Star Online: "My son would have done no wrong. No authority contacted me to say they will be searching my son's house. Even if they do, we have nothing to hide.''

The father said he was due to visit his son's new home this month but rescheduled after Khairul was called to Beijing for work.