HANOI, March 11 ― Investigators from at least nine countries hunting for a missing Malaysian passenger jet are sorting through a jumble of facts and theories that so far don’t add up into a clear explanation of what happened to the plane.

Malaysian Airline System Bhd.’s Flight 370 disappeared more than three days ago en route from Kuala Lumpur to Beijing with 239 people aboard. The pilots never signalled trauma or danger before losing radio contact between Malaysia and Vietnam.

With today’s technology, it’s unusual for a plane to vanish without a distress call. When they do disappear suddenly, it’s typically because of an event such as a massive engine failure or explosion. That however would create widely scattered debris, and search teams haven’t been able to recover any remnants. That the plane was a Boeing Co. 777, one of the most reliable jets in the air, only adds to the puzzle.

“It’s becoming increasingly mysterious as the days go by,” said Shukor Yusof,an analyst at Standard & Poor’s in Singapore. “Now we’re into the fourth day and we still haven’t gotten anything. That’s why it makes this deeply, deeply baffling.”

As a new day of search begins, none of the potential leads for finding the plane had panned out. Vietnamese authorities reported sighting what appeared to be a life raft and recovered the object only to find it was a moss-covered cable. There were reports that a window or door fragment from a plane had been spotted, yet the pieces were never recovered. Malaysia investigators tested samples from an oil slick once seen as a crash marker and found they were in fact marine fuel.

Broadening hunt

Search teams are now broadening their hunt, dispatching ships to check debris in the South China Sea after focusing on the Gulf of Thailand. That broadens the inquiry farther from the flight’s path. Vietnam has deployed a total of 10 aircraft to search for the missing plane.

The latest sighting came as the search for Flight 370 left authorities confounded as to how a jet with one of the industry’s best safety records could vanish from radar without a trace, even after days of patrols by surface vessels, planes and helicopters.

“This was a relatively long flight going over large areas of water,” said John Hansman, a professor of aeronautics and astronautics at Massachusetts Institute of Technology. “So there’s a reasonably large area that has to be searched to find something. I’m convinced something will turn up in the next few days.”

False passports

Closed-circuit television footage of two travelers with stolen passports gave investigators another set of clues to examine. Austria and Italy said the passports were stolen from their nationals. The Royal Thai Police is probing the two thefts, which occurred in Phuket in 2012 and last year, spokesman Piya Uthayo said in Bangkok.

“We are trying to ascertain if the two holders of false passport entered Malaysia, legally or illegally,” Inspector- General of Police Khalid Abu Bakar said in a mobile-phone text message. The Financial Times reported that Malaysian authorities have given US investigators biometric details on the travelers with the stolen passports.

Ticket numbers

Tickets purchased with the pilfered passports on the flight, which belonged to Luigi Maraldi of Italy and Christian Kozel of Austria, had consecutive numbers, according to the Chinese e-ticket verification system Travelsky.

Men using the passports purchased the tickets on March 6 from Six Star Travel Co. in Pattaya, Thailand, city police Commander Supachai Phuykaeokam said by phone. The person with Maraldi’s documents had a final destination of Copenhagen, while Frankfurt was listed as the last stop for the person posing as Kozel, the commander said.

An officer at Six Star Travel declined to comment. The Financial Times cited a travel agent as saying she was asked to arrange the trips for the two men by an Iranian contact. Neither Maraldi nor Kozel was on the Malaysian aircraft, their governments said.

Evidence that typically might be spotted after a terrorist incident is lacking so far, said two US officials. At the same time, the absence of clues isn’t enough to rule out such an attack, said the officials, who asked not to be identified while discussing intelligence activities.

No anomalies

The early warning system for the North American Air Defense Command detected no anomalies related to Flight 370, said one of the officials. Norad’s infrared and visual imagery can pick up heat sources such as explosions and missile launches, the official said.

US intelligence agencies also haven’t turned up a burst of chatter online or on the airwaves of the type that often follows an attack, the second official said.

Before takeoff from Kuala Lumpur, Malaysian Airline removed the baggage of five passengers who didn’t board after checking in, said Azharuddin Abdul Rahman, director general of Malaysia’s Department of Civil Aviation. “There are issues about the passengers that did not fly on the aircraft,” he said without elaborating.

Chinese travellers accounted for the largest group aboard Flight 370, with 153 people, and that country’s government prodded the carrier to hasten the inquiry. Also aboard were three US citizens, according to the US State Department. The US Navy sent two destroyers and aircraft into the region, according to the Defense Department.

Flight path

Flight 370 departed Kuala Lumpur at about 12.41am local time March 8 and was scheduled to land in Beijing at 6.30am. Security screening was performed as usual, Malaysia Airports Holdings Bhd. said. Controllers lost radar contact about an hour into the flight as the plane neared Vietnamese airspace.

The aircraft, which disappeared without providing any distress signal, may have made an “air turn-back,” said Malaysian Acting Transport Minister Hishammuddin Hussein. That means the plane may have deviated from its planned route, said Malaysian Air Chief Executive Officer Ahmad Jauhari Yahya.

Finding the jet’s flight-data and cockpit-voice recorders, the units known collectively as an aircraft’s black box, would help investigators unravel what happened in the final moments of Flight 370.

Honeywell’s equipment

Honeywell International Inc. manufactures the 777’s recorders and the so-called emergency locator transmitter, a separate beacon that sends a homing signal in the event of a sharp impact such as a crash. The black-box unit emits a ping when underwater, where the ELT won’t work.

Steve Brecken, a Honeywell spokesman, declined to comment beyond a company statement expressing sympathy for relatives and loved ones of Flight 370’s passengers and crew.

A team from the US National Transportation Safety Board is in Malaysia, joined by specialists from the Federal Aviation Administration and Boeing.

While Muslim-majority Malaysia hasn’t seen any recent major terrorist attacks on home soil, it has been used as a transit and planning hub, according to a 2012 report by the US State Department. China has occasionally been the target of what it calls terrorist attacks by Uighurs, a mainly Muslim ethnic group from the nation’s northwest Xinjiang region.

Malaysian Air said it dispatched more than 150 “Go Team” members, consisting of senior managers and caregivers, to Beijing to attend to passengers’ families. Allianz SE, Europe’s biggest insurer, said it provides liability coverage to the airline. ― Bloomberg