(CNN) -
Uncertainly over the fate of missing Malaysia Airlines Flight MH370 was further compounded Saturday by reports that two men whose names matched those on the passenger manifest had reported their passports stolen.
After the airline released a manifest of the 239 people on the plane, Austria denied that one of its citizens was on the flight as the list had stated. The Austrian citizen was safe and sound, and his passport had been stolen two years ago, Austrian Foreign Ministry spokesman Martin Weiss told CNN.
Similarly, Italy's foreign ministry confirmed that no Italians were on the flight, even though an Italian was listed on the manifest. Malaysian officials said they were aware of reports that the Italian's passport was also stolen but had not confirmed it.
On Saturday, Italian police visited the home of the parents of Luigi Maraldi -- the man whose name appeared on the manifest -- to inform them about the missing flight, said a police official in Cesena, in northern Italy.
Maraldi's father, Walter, told police that he had just spoken to his son, who was fine and not on the missing flight, said the official, who is not authorized to speak to the media. Maraldi was vacationing in Thailand, his father said. The police official confirmed that Maraldi had reported his passport stolen in Malaysia last August and that he had obtained a new passport.
The stolen passports raised concerns about the possibility of terrorism.
"It's an important clue that needs to be followed up on," said Tom Fuentes, a former assistant director of the FBI and CNN law enforcement analyst. "If the individuals that previously owned those passports weren't passengers, who was? That's going to be an important part of the investigation."
A U.S. intelligence official said authorities are aware of the lost or stolen passports used by passengers on the missing flight.
"No nexus to terrorism yet," the official said, "although that's by no means definitive. We're still tracking."
Malaysian authorities reiterated during a news conference that they are not ruling anything out regarding the missing aircraft.
Fuentes said that Interpol, the international law enforcement agency, maintains an extensive database of lost and stolen passports. The use of the stolen passports by passengers on the Malaysia Airlines flight should have been checked against that database by airline officials, he said.
"Now the question here becomes, did the authorities in Malaysia, the airport in Kuala Lumpur, did they make inquiry of that database," Fuentes said. "Is that system set up to make an automatic inquiry if someone is using a previously reported stolen document? That should come up right away if they check that database. Not every country that belongs to Interpol automatically does that."
In the United States, Fuentes said, passports are routinely checked against the Interpol database, which contains more than 30 million records.
No one is sure what happened to Malaysia Airlines Flight MH370. Air traffic controllers lost track of it after it left Kuala Lumpur, the capital of Malaysia, on its way to Beijing on Friday. The plane was two hours into its flight, cruising during what experts consider to be the safest part of the journey, when it vanished.
Greg Feith, a former investigator with the National Transportation Safety Board, told CNN that there were multiple scenarios of what could have gone wrong, including structural problems with the wings or fuselage.
"Of course, you also have to look at in that part of the world and around the world there is still a potential for a terrorist act or an intentional act that could have rendered the airplane incapacitated," he said.
He added: "Whatever happened, happened very quickly. For them to have lost two-way radio communication with [air traffic control], two-way radio communication with the company, and to lose any kind of radar data with ground control facilities means that the airplane was compromised in a very quick manner and it may have been well beyond the control of the crew to keep the airplane under control and make any kind of emergency distress call or emergency landing."