Malaysian Airlines flight MH370 disappeared six days ago and an international search and rescue effort in waters around Southeast Asia has failed to find a shred of evidence in one of the biggest aviation mysteries in history.
With little solid information to go on, authorities are investigating all 227 passengers and 12 crew for possible sabotage, although they stress no such evidence has come to light.
But it has brought Captain Zaharie Ahmad Shah, 53, and his First Officer Fariq Abdul Hamid, 27, under scrutiny.
An Australian television report made waves this week by broadcasting an interview with a young South African woman who said Fariq and another pilot colleague invited them into the cockpit of a flight he co-piloted from Phuket, Thailand to Kuala Lumpur in 2011.
Passengers have been prohibited from entering cockpits during a flight since the 9/11 attacks on the United States. Malaysia Airlines said it was "shocked" by the reported security violation, but that it could not verify the claims.
- 'Good boy' -
Fariq, who joined the airline at the age of 20, studied piloting at a flight school on the Malaysian resort island of Langkawi.
The son of a high-ranking official in the public works department of a Malaysian state, he is a mild-mannered "good boy" who regularly visited his neighbourhood mosque outside Kuala Lumpur, said the mosque's imam, or spiritual leader.
Fariq also attended occasional Islamic courses, said Ahmad Sharafi Ali Asrah.
He rejected the account of the supposed cockpit security breach.
"This story doesn't make sense and I feel it's just an effort to discredit Fariq or the airlines," Ahmad Sharafi said.
"He is a good boy and keeps a low profile."
Fariq had a brief brush with fame when he appeared in a CNN travel segment with the network’s correspondent Richard Quest in February, in which Fariq helped fly a plane from Hong Kong to Kuala Lumpur.
The segment portrayed Hamid’s transition to piloting the Boeing 777-200 after having completed training in a flight simulator.
"It was interesting to watch the way he brought the aircraft in to land," Quest said, according to the CNN website, calling Fariq's technique “textbook-perfect”.
- Mr Fix-it -
The far more seasoned Zaharie joined MAS in 1981 and had logged 18,365 hours of flying time.
Online tributes in Malaysia portray a man so fond of flying that he assembled his own flight simulator so that he could indulge his passion at home.
The webpage, which has garnered more than 400 comments largely from well-wishers, shows pictures of the complex set-up including Zaharie posing in front of it.
Zaharie also has a YouTube channel to which he has uploaded videos showing him cheerfully explaining how to fix an air-conditioner, patch damaged windows, and other DIY projects.
Malaysian media reports have quoted colleagues as calling Zaharie a "superb pilot", who also served as an examiner, authorised by the Malaysian Civil Aviation Department, to conduct simulator tests for pilots.
Malaysia Airlines has declined to offer details on the two men, and no other red flags have emerged publicly. Authorities have denied media reports that investigators raided their homes .
- Shadow of suspicion -
The near-total lack of information pointing to the plane's fate necessarily means that authorities need to examine the spectre of possible wrongdoing by those who could have held its fate in their hands, analysts said.
The mysterious disappearance of the plane from radar has led to speculation over whether its communications were deliberately shut down by someone on board, one of many theories bandied about.
In three of the four flights used for the 9/11 attacks, hijackers who seized control of the aircraft are believed to have manually turned off each plane’s transponder, which sends flight data back to air-traffic control.
Terence Fan, an aviation expert at Singapore Management University, cited the crash of EgyptAir Flight 990 in October 1999 in the Atlantic Ocean -- which killed 217 people -- as an example of a crash allegedly deliberately caused by a pilot.
A US investigation said the first officer crashed the jet when the captain went on a break, findings disputed by Egyptian officials.
"I am not saying such a scenario happened here, we don't have any evidence at all, but this is one possible scenario," he said.
"Certainly, the pilots play a very crucial role."