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.