KUALA LUMPUR, Malaysia (AP) — Vietnamese aircraft spotted what they suspected was one of the doors of a missing Boeing 777 on Sunday, while troubling questions emerged about how two passengers managed to board the ill-fated aircraft using stolen passports.

Interpol confirmed it knew about the stolen passports but said no authorities checked its vast databases on stolen documents before the Boeing jetliner departed Saturday en route from Kuala Lumpur to Beijing.

Warning “only a handful of countries” routinely make such checks, Interpol secretary general Ronald Noble chided authorities for “waiting for a tragedy to put prudent security measures in place at borders and boarding gates”.

More than two days after Malaysia Airlines Flight MH370 went missing, the final minutes before its disappearance remained a mystery. The plane lost contact with ground controllers somewhere between Malaysia and Vietnam.

However, searchers in a low-flying plane spotted an object that appeared to be one of the plane’s doors, the state-run Thanh Nien newspaper said, citing the deputy chief of staff of Vietnam’s army, Lt Gen Vo Van Tuan.

Two ships from the maritime police were headed to the site in waters about 60 miles (90 kilometres) south of Tho Chu island, in the same area where oil slicks were spotted Saturday.

“From this object, hopefully (we) will find the missing plane,” Tuan said.

The missing jetliner apparently fell from the sky at cruising altitude in fine weather, and the pilots were either unable or had no time to send a distress signal — unusual circumstances under which a modern jetliner operated by a professional airline would crash.

Authorities were checking on the identities of the two passengers who boarded the plane with stolen passports. On Saturday, the foreign ministries in Italy and Austria said the names of two citizens listed on the flight’s manifest matched the names on two passports reported stolen in Thailand.

“I can confirm that we have the visuals of these two people on CCTV,” Malaysian Transport Minister Hishammuddin Hussein said at a news conference late Sunday, adding that the footage was being examined. “We have intelligence agencies, both local and international, on board.”