American investigators have settled on three primary theories to explain the disappearance of Malaysia Airlines Flight 370, a senior U.S. official told ABC News tonight.
The leading theories are:
1. Pilot suicide or other human action;
2. Fire or catastrophic mechanical malfunction;
With terrorism all but ruled out, however, investigators still are leaning toward the vanishing of the passenger jet with 239 travelers and crew aboard as "a deliberate act," the official said.
"That's pretty much what everyone thinks," the senior U.S. official, who receives frequent updates on the investigation, told ABC News.
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The Obama administration has been cautious all along in the sparse public statements they have made over the past two weeks, beyond pledging to assist the Malaysian government.
Asked about lithium batteries known to be aboard MH370, the official said the amount and weight of the potentially flammable cargo "has been classified" secret by investigators but said it was "comparable to the Dubai jet," referring to UPS Flight 6, which crashed in the United Arab Emirates in late 2010.
Still, the focus of the probe, as ABC's Brian Ross was told a week ago by another senior official, remains primarily on what happened inside the cockpit rather than in the cargo hold, noting that the aircraft is believed to have flown more than seven hours after taking off from Kuala Lumpur on March 7.
Finding out what happened to the jet and how it vanished seemingly into thin air must be determined by the U.S. in order to ensure it isn't repeated or becomes a national security vulnerability, the official added.
The official spoke after the Chinese government released a satellite image showing a new object floating in the water today, another lead for search crews trying to find the missing plane.
China's State Administration for Science, Technology and Industry for National Defense released the photo of the object, which is reportedly 74 feet long and 43 feet wide. It was spotted about noon Tuesday in the southern Indian Ocean, about 75 miles southwest of the region where two objects released by Australia were previously seen.
The news of the object interrupted a press conference Malaysian officials held, as Malaysia's Acting Transport Minister Hishammuddin Hussein was given a piece of paper containing details about the object. He concluded the press conference early as reporters peppered him with questions about the development.
Before receiving the note, Hishammuddin told reporters that China, India, Pakistan, Myanmar, Laos and Kyrgyzstan hadn't found anything related to the plane in the northern search corridor.
Malaysia Airlines Flight 370 disappeared on March 8.
Search crews again came up empty during the third day of the search in the desolate southern Indian Ocean. There was no reports of any sign of the missing plane or the two objects spotted by satellite in the area six days ago.
The search area covered Saturday, an area of 36,000 square kilometers, included the area where the new object was spotted by Chinese satellites but the object wasn't found, according to the Australian Maritime Safety Authority.
A New Zealand P3 Orion aircraft with special observation equipment dropped a marker buoy to track the movements of any material that might be in the water. Spotters saw small objects but aircraft diverted to the location found only seaweed, said Australian officials.
Six planes took off to search for possible parts of the plane, checking waters about 1,500 miles southwest of Perth. As other ships headed toward the area to contribute to the search, the British Ministry of Defense told ABC News that the British HMS Echo, a hydrographic survey ship, had yet to leave the Persian Gulf and would not arrive for at least 10 days.
A Norwegian merchant ship that had been asked to divert from its planned course to help search the area was allowed to continue on its planned route to Melbourne, said the Australian Maritime Safety Authority.
Weather is adding further difficulty to the search efforts. A tropical storm is headed for the search area, Acting Australian Prime Minister Warren Truss said, with strong winds expected.
Satellite images released by Australia showed two objects – the biggest about 80 feet long – in the southern Indian Ocean. Those images were taken March 16, but the search in the area did not start until Thursday, March 20, because it took time to analyze the images.
During a news conference, Truss questioned whether the delay meant search crews missed their chance to find the objects.
"The fact that it's six days ago that this imagery was captured does mean, clearly, what objects that were there are likely to have moved a significant distance as a result of currents and winds. It's also possible of course that they've just drifted to the bottom of the ocean bed," he said.
Truss remained optimistic about the search efforts.
"It is a very remote area, but we intend to continue the search until we're absolutely satisfied that further searching would be futile. And that day is not in sight," he said.
Aircraft in the Indian Ocean included two ultra-long-range commercial jets and four P3 Orions, the Australian Maritime Safety Authority said.
Because of the distance to the area, the Orions will have enough fuel to search for two hours, while the commercial jets can stay for five hours before heading back to the base.
Two merchant ships were in the area, and the HMAS Success, a navy supply ship, was due to arrive late Saturday afternoon. Weather in the search zone was expected to be relatively good, with some cloud cover.
Two Chinese aircraft were expected to arrive in Perth Saturday to join the search, and two Japanese planes will arrive Sunday. A small flotilla of ships from China is still several days away. The Malaysian plane passengers included 154 Chinese.
Malaysia – which is overseeing the overall search efforts – asked the U.S. for undersea surveillance equipment to help in the search, said Rear Adm. John Kirby, a Pentagon spokesman. Defense Secretary Chuck Hagel promised to assess the availability of the technology and its usefulness in the search, Kirby said.
The Pentagon says it has spent $2.5 million to operate ships and aircraft in the search and has budgeted another $1.5 million for the efforts.
There is a limited battery life for the beacons in the cockpit-voice and flight-data recorders — about 30 days, said Chuck Schofield, vice president of business development for Dukane Seacom Inc. He said it's "very likely" that his company made the beacons on the missing jet. The devices work to a depth of 20,000 feet, with a signal range of about 2 nautical miles, depending on variables like sea conditions. The signals are located using a device operated on the surface of the water or towed to a depth.
Experts say it is impossible to tell if the grainy satellite images of the two objects were debris from the plane. But officials have called this the best lead so far in the search that began March 8 after the plane vanished over the Gulf of Thailand on an overnight flight to Beijing.
For relatives of those aboard the plane, which went missing March 8, hope was slipping away, said Nan Jinyan, sister-in-law of passenger Yan Ling.
"I'm psychologically prepared for the worst and I know the chances of them coming back alive are extremely small," said Nan, one of dozens of relatives gathered at a Beijing hotel awaiting any word about their loved ones.
Malaysian authorities have not ruled out any possible explanation for what happened to the jet but have said the evidence so far suggests it was deliberately turned back across Malaysia to the Strait of Malacca, with its communications systems disabled. They are unsure what happened next.
Police are considering the possibilities of hijacking, sabotage, terrorism or issues related to the mental health of the pilots or anyone else on board.
The Associated Press contributed to this report.