When Malaysia Airlines Flight 370 vanished into thin air over the weekend, it left officials grappling with several perplexing questions: What happened to the plane? Where was it? And who were the two men who used stolen passports to get on board?
While answers to the first two mysteries continue to bedevil authorities, they were able to piece together the third puzzle Tuesday.
The two men were Iranians who used the passports to fly from Malaysia to Europe. Their tickets were purchased by another Iranian, officials said.
But, said police, there's no evidence to suggest the men had anything to do with the plane's disappearance.
"The more information we get, the more we're inclined to conclude that it was not a terrorist incident," Interpol Secretary General Ronald Noble told reporters Tuesday in France.
Here's what we know about what happened, how it happened and why.
WHO ARE THEY?
The two passengers are Delavar Seyed Mohammad Reza, 29; and Pouri Nourmohammadi, 18.
They entered Malaysia on February 28 using valid Iranian passports, but ones that were not listed on Interpol's database.
CNN obtained an iReport photo of the two men with two of their friends, believed to have been taken on Saturday before the plane disappeared. CNN has blurred the faces of the other two men to protect their identity.
To fly out of Malaysia, Reza and Nourmohammadi used passports that were stolen in Thailand -- a booming market for stolen passports. The passports belonged to citizens of Italy and Austria.
"Thailand remains a robust venue for the sale of high-quality false passports (which includes altered stolen passports) and other supporting documentation," said Paul Quaglia, who has been working in the region as a security and risk analyst for 14 years.
The Italian, Luigi Maraldi, 37, told reporters he'd reported his passport stolen in August.
The Austrian, Christian Kozel, 30, had his stolen in July 2013.
Authorities don't know yet if Reza and Nourmohammadi were involved in the passports' theft or how they came to possess them.
HOW IT HAPPENED?
On Saturday, Reza used the Italian's passport; Nourmohammadi used the Austrian's.
According to Thai police officials, an Iranian man by the name of Kazem Ali bought one-way tickets for the two men, describing them as friends who wanted to return home to Europe. While Ali made the initial booking by telephone, either Ali or someone acting on his behalf paid for the tickets in cash, according to police.
The tickets were apparently purchased at the same time from China Southern Airlines in Thailand's baht currency at identical prices, according to China's official e-ticket verification system Travelsky.
The ticket numbers are contiguous, indicating they were issued together.
Both were for travel from Kuala Lumpur to Amsterdam via Beijing.
The ticket using the Italian passport then continued on to Copenhagen, Denmark.
The ticket on the Austrian passport ended in Frankfurt, Germany.
Nourmohammadi was hoping to emigrate to Germany. His mother had been expecting him to arrive in Frankfurt and contacted authorities when he didn't show up, said Malaysian Inspector General of Police Khalid Abu Bakar.
"If you read what the head of Malaysia police said recently, about (Nourmohammadi) ... wanting to travel to Frankfurt, Germany, to be with his mother, (this) is part of a human smuggling issue and not a terrorist issue," Interpol's Noble said.
Interpol says the stolen passports were in its database. But no country had checked them against Interpol's list. It is countries, not airlines, that have access to Interpol's data, and many governments don't routinely check passports against the database.
WHY IT HAPPENED?
One can only guess. But Phil Robertson, deputy director of the Asia Division of Human Rights Watch, has a plausible explanation.
"After the Green Revolution in Iran for human rights and democracy was crushed by Iranian authorities, there were many Iranians who fled to Malaysia," he told CNN's Kristie Lu Stout.
Malaysia is a country where many Middle Easterners don't need a visa to enter -- making it an easy destination for those from restive places like Iran or Syria.
The problem arises when they try to leave for other countries -- places that do require visas. And sometimes those places can be selective as to who gets them.
"They have the money to move, it's likely they want to get out," Robertson said. "A stolen passport can be one way to do it. Unfortunately, this is quite common."
And how do they do they go about getting such passports?
"Often persons like this, if they are going to make a play to go to somewhere like Germany or other parts of Europe, they would need some sort of broker to help them make the arrangements," he said. "So it's very possible you could have
some sort of migrant smuggling group that's involved with this."