BEIJING — Frustration mounted Monday over what has become one of the most perplexing aviation disasters in history, as the search for a vanished Malaysia Airlines passenger jet dramatically expanded in its third day.
Hopes for a breakthrough were dashed when Malaysian authorities said oil found on the ocean surface had been tested and found not to have come from the jetliner. Various pieces of flotsam picked up in the vicinity of the plane’s last known location were also found to be unconnected.
“This unprecedented missing aircraft mystery — as you can put it — it is mystifying,” Azharuddin Abdul Rahman, director general of Malaysia’s Department of Civil Aviation, said at a news conference in Kuala Lumpur.
“To confirm what happened that day on this ill-fated aircraft, we need hard evidence,” he said. “We need concrete evidence. We need parts of the aircraft for us to analyze, for us to do forensic studies.”
About 40 ships and 34 aircraft from nine countries are combing a vast area of ocean in the Gulf of Thailand and the South China Sea, northeast of Malaysia toward Vietnam. The search grid has expanded into areas well beyond the plane’s intended northeasterly flight path toward China. Authorities are now looking even at areas in the Andaman Sea, on the western side of the Malaysian peninsula.
Two oil slicks, between 6 and 9 miles long, consistent with fuel left by a downed jetliner, were located Saturday in the region where the plane vanished. But tests Monday concluded that they were not connected to the plane.
For the plane to have crashed into the Andaman Sea would imply that it had somehow turned back and crossed the entire Malaysian peninsula without being detected by radar operators.
Malaysian authorities said Sunday that the plane may have turned around before disappearing from radar without a distress call. If true, aviation experts said, this could offer a clue as to why no debris had yet been found.
Possible reasons the plane turned include pilot action, hijacker command, or a structural failure. In a vacuum of hard evidence about what went wrong, speculation also turned to the possibility of pilot suicide, an extraordinarily rare occurrence that has taken down two commercial airliners in recent years.
Speculation that terrorists could have brought down the plane were fueled by reports that two men boarded using stolen passports, but experts said this could easily have been a coincidence.
On Monday, Azharuddin said closed-circuit television footage showed that the men passed through normal security checks at the airport and were not of Asian appearance. Officials also said they have shared “biometric and visual” information about the men with US intelligence agents.
Authorities on Monday questioned travel agents at a beach resort in Pattaya, Thailand, about the two men, the Associated Press reported. Investigators have not made their names public.
Thailand police Lieutenant Colonel Ratchthapong Tia-sood said the travel agency was contacted by an Iranian man known only as ‘‘Mr. Ali’’ to book the tickets for the two men, the AP said.
Luigi Maraldi, 37, of Italy and Christian Kozel, 30, of Austria were initially listed among the plane’s passengers, but both were subsequently found to be safe — and to have reported their passports stolen long ago.
Booking information accessed through the KLM website showed that the passengers using the passports had adjacent ticket numbers and were both booked on a subsequent flight from Beijing to Amsterdam.
One, traveling under Maraldi’s name, was to continue to Copenhagen and the other to Frankfurt. Azharuddin said investigators were looking at whether the two men who boarded were linked to a “stolen passports syndicate.”
Earlier, he said five other passengers checked in for the flight but never boarded. He insisted that their baggage was removed before the plane took off.
The Malaysia Airlines flight reportedly was being tracked by radar when its transponder went dark. There were no radio transmissions to indicate that anything was amiss aboard the plane. Both the transponder signals and radio communication are controlled by the pilot, who can also turn off the voice recorder.
That’s what investigators believe happened aboard SilkAir Flight 185 before it spiraled to the ground in Indonesia in 1997, killing 97 passengers and seven crew members.
EgyptAir Flight 990 also has received renewed attention after the Malaysia Airlines flight went missing. The 1999 Egyptian flight crashed into the Atlantic south of Nantucket, killing 217 people. US investigators concluded that the crash was caused by crew member Gameel Al-Batouti.
In a phone interview Monday, a spokesman for the US Navy’s Seventh Fleet, Commander William Marks, confirmed that the USS Pinckney has joined the search for the Malaysia Airlines jet. Marks told the BBC that the destroyer and the helicopters it carries have infrared, sonar, and other search capabilities and can also listen for any signal emitted from the plane’s black box.
On Monday, hopes briefly centered on an object that authorities said might have been a lifejacket. But when a Vietnamese helicopter recovered the piece of flotsam, it was identified as “a moss-covered cap of a cable reel,” the Civil Aviation Authority of Vietnam said.