While the whereabouts of Malaysia Airlines flight MH370 are still unknown, new details are surfacing about the plane’s mysterious disappearance. Several news outlets report that two passengers aboard the Boeing 777-200 weren’t who they said they were, sparking fears of a possible terrorist plot.

According to the New York Times, the names of two passengers listed on the flight’s manifest, passengers 63 and 101, match the names of two passports that were stolen in Asia a few years ago. The passports belonged to two men – one Austrian and one Italian – who authorities have confirmed were not on Malaysia Airlines flight MH370 and are in fact alive. The Italian man, Luigi Maraldi, told reporters that he lives in Bangkok.

The passports were both reported stolen in Thailand. According to China Southern, which operates a codeshare on the flight, both passengers using the stolen passports had booked through its ticketing office, the Telegraph reports.

“We believe that the name and passport were used by an unidentified person to board the plane,” a spokesman for the Austrian foreign ministry told NBC News.

Authorities say that while the stolen passports certainly raise questions, investigators are far from calling the flight’s disappearance an act of terror.

“At this time, we have not identified this as an act of terrorism,” a senior American intelligence official, who remained anonymous, told the New York Times. “While the stolen passports are interesting, they don’t necessarily say to us that this was a terrorism act.”

Another U.S. official told NBC News that investigators have not found a “nexus to terrorism,” but that the search is still in its early stages and “that it’s by no means definitive.”

Malaysia Airlines flight MH370 departed from Kuala Lumpur at 12:41 a.m. local time Saturday morning and was scheduled to land in Beijing at 6:30 a.m local. Air traffic control lost contact with the aircraft carrying 227 passengers, most of whom were Chinese, and 12 crew members two hours after the flight left Kuala Lumpur, but the last radar contact was at 1:19 a.m., just 40 minutes after the flight began.

A spokesman for Malaysia Airlines confirmed Saturday evening that air traffic control in Malaysia last spoke with the flight crew at around 1:30 a.m., but that the plane did not disappear from air traffic control systems until an hour and 10 minutes later.

Investigators fear the Boeing B777-200 aircraft crashed into the South China Sea somewhere between Malaysia and Vietnam. Search crews from Malaysia, Vietnam, China and the U.S. were dispatched to try and recover wreckage from the plane. All they found was an oil slick in the search area, which authorities suspect may be from the downed Boeing aircraft.

Malaysia Airways contacted the passengers’ next of kin and asked them to come to the airport with their passports to prepare to fly to a potential crash site.

Reports indicate that Malaysia Airlines’ safety record is consistent with other airlines. The airline suffered two fatal crashes in its history, one in 1977 and one in 1995. The one in 1977 killed all 93 passengers and seven crew members, and was caused by a hijacking.