Amid the multitude of questions about the fate of missing Malaysia Airlines Flight 370, one small part of the story became clearer Tuesday when police said they have identified one of the passengers who used a stolen passport to board the plane. And it's unlikely, they said, that he was part of a terrorist group.
He is a 19-year-old Iranian man, named Pouria Nour Mohammad Mehrdad, who was trying to emigrate to Germany, said Inspector General Khalid Abu Bakar of the Royal Malaysian Police.
The use of the stolen passports by two passengers on the plane, which vanished from the skies early Saturday, raised fears that its disappearance could be linked to terrorism.
But Khalid said authorities don't think the young Iranian posed a threat.
"We have been checking his background. We have also checked him with other police organizations of his profile and we believe that he is not likely to be a member of any terrorist group," Khalid said.
After he failed to arrive in Frankfurt, the final destination of his ticket, his mother contacted authorities, Khalid said. According to ticketing records, the ticket to Frankfurt was booked under a stolen Austrian passport.
Authorities are still investigating the identity of the other passenger who used a stolen passport.
The bigger piece of the puzzle
The identification of one of the men helps peel away a thin layer of the mystery surrounding the passenger jet, which disappeared about an hour into its flight from Kuala Lumpur to Beijing.
But in the bigger puzzle of the missing plane's whereabouts, there were no reports of progress Tuesday.
Every lead that has raised hopes of tracing the commercial jet and the 239 people on board has so far petered out.
The challenge facing those involved in the huge, multinational search is daunting; the area of sea they are combing is vast.
And they still don't know if they're looking in the right place.
"As we enter into Day 4, the aircraft is yet to be found," Malaysia Airlines said in a statement Tuesday.
Days, weeks or even months
Over the past few days, search teams have been scouring tens of thousands of square miles of sea around the area where the plane was last detected, between the northeast coast of Malaysia and southwest Vietnam.
They have also been searching off the west coast of the Malaysian Peninsula, in the Strait of Malacca, and north into the Andaman Sea. The airline said Tuesday that authorities are still investigating the possibility that the plane might have tried to turn back toward Kuala Lumpur.
The search also encompasses the land in between the two areas of sea.
But it could be days, weeks or even months before the searchers find anything that begins to explain what happened to the plane, which disappeared early Saturday en route to Beijing.
In the case of Air France Flight 447, which disappeared over the Atlantic in 2009, it took five days just to locate the first floating wreckage.
And it was nearly two years before investigators found the bulk of the French plane's wreckage, and the majority of the bodies of the 228 people on board, about 12,000 feet below the surface of the ocean.
The Gulf of Thailand, the area where the missing Malaysian plane was last detected is much shallower, with a maximum depth of only 260 feet and an average depth of about 150 feet.
"If the aircraft is in the water, it should make recovery easier than the long and expensive effort to bring up key parts of the Air France plane," Bill Palmer, an Airbus A330 captain for a major airline, wrote in an opinion article for CNN.
But if Flight 370 went down farther west, it could have ended up in the much deeper waters of the Andaman Sea.
No possibilities ruled out
Aviation officials say they haven't ruled out any possibilities in the investigation so far. It's hard for them to reach any conclusions until they find the plane, along with its voice and data recorders.
Malaysian police are focusing on four particular areas, Khalid said Tuesday: hijacking, sabotage, psychological problems of the passengers and crew, and personal problems among the passengers and crew.
He said police were going through the profiles of all the passengers and crew members.
Malaysia Airlines Chief Executive Ahmad Jauhari Yahya told CNN's Jim Clancy that those involved in the search for the plane are determined to carry on.
"We just have to be more resolved and pay more attention to every single detail," he said Tuesday. "It must be there somewhere. We have to find it."