Rescue helicopters and ships completed more than two days of fruitless search for the Malaysia Airlines jet that disappeared over the sea with 239 people on board en route Beijing from here on Saturday.

On Monday, search teams rushed to investigate a yellow object that looked like a life raft floating in the ocean, but it turned out to be moss-covered trash. With no confirmation that the Boeing 777 crashed, hundreds of distraught relatives waited anxiously for news. Thai police and Interpol questioned the proprietors of a travel agency in the resort town of Pattaya that sold one-way tickets to two men who boarded flight MH370 using stolen passports.

Malaysia’s police chief was quoted by local media as saying that one of the men had been identified. Civil aviation chief Azharuddin Abdul Rahman declined to confirm this, but said they were of “non-Asian” appearance, adding that the authorities were looking at the possibility the men were connected to a stolen passport syndicate.

Experts say possible causes of the apparent crash include an explosion, catastrophic engine failure, terrorist attack, extreme turbulence, pilot error or even suicide.

On Sunday afternoon, a Vietnamese plane spotted a rectangular object that was thought to be one of the missing plane’s doors, but ships working through the night could not locate it. Malaysian maritime officials found oil slick in the South China Sea and sent a sample to a lab to see if it came from the plane. Tests showed the oil was not from an aircraft, Mr. Rahman said.

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