KUALA LUMPUR, Malaysia (CBSNewYork/CBS News/AP) -- It has been one week since the search for missing Malaysia Airlines flight MH370 started.
There have been plenty of theories over the last seven days about what happened to the missing plane, but still no concrete evidence, CBS 2's Christine Sloan reported.
As CBS 2's Tony Aiello reported, piracy and pilot suicide are among the scenarios under study.
Investigators still have no idea where the plane is, but there is growing evidence the plane may have been intentionally sent thousands of miles off its original course.
The search expanded east and west on Friday after U.S. officials said the plane was emitting signals to satellites for hours after its last contact with air traffic control over the South China Sea.
Malaysian officials insisted that investigators had yet to reach a definitive conclusion on what radar and satellite data showed, and said the search was being expanded because efforts in current areas have not found any wreckage from the Boeing 777.
The possibility that the plane, carrying 239 people, flew many hundreds of miles beyond its last known location without any contact with the ground has strengthened speculation that its transponders and other communication devices were turned off deliberately.
That opens the possibility that one of the pilots, or someone with flying experience, wanted to hijack the plane for some later purpose, kidnap the passengers or commit suicide by plunging the aircraft into the sea.
"You have a problem with the course of the aircraft deliberately taken off course that only leads to one conclusion: It was a criminal act or a terrorist act," former FBI analyst Steven Rogers told Sloan.
"I question as to who might have been in the cockpit at the time when that aircraft had the, particularly the transponder turned off," retired pilot Mark Weiss told CBS News.
Given the amount of fuel it had on board, the plane could in theory have reached anywhere in a large swath of South and Southeast Asia. In the absence of more information on its movements, finding it could be a massive task.
The United States and 12 other countries are aiding in the search with 57 ships and 48 aircraft scouring the area for any sign of the missing plane, Aiello reported.
CBS News' Bob Orr reported Thursday that two communication systems on the flight were shut down sequentially in the moments before the plane disappeared from radar on Saturday; a data system and two transponders which relayed information about the jet's speed, altitude and location. That suggests it was done on purpose, Aiello reported.
While a cascading electrical problem could feasibly cause that kind of staged electrical failure, Orr said it's also entirely possible somebody on the plane intentionally turned off the systems. And investigators say there's further evidence suggesting the jet did not crash immediately after being lost on radar; a transmitter on the plane tried for another four hours to ping satellites. That's an indication to analysts that the jet continued to fly for some time -- possibly as far as 2,500 miles from where it was last detected.
"I mean, could we construct a theory where that might have happened with a progressive fire or something? Yes, but it would be very, very far out," said aviation analyst John Nance. "Much more likely a human being was pulling circuit breakers at a sequential time."
Transponders are sometimes switched to "off" or "standby" on approach to busy airports, Aiello reported. Experts say turning communications systems off in the middle of a flight over a body of water is highly unusual.
"Clearly, if all the power is lost to the aircraft, or something happened to take out that part of the electrical system that would turn it off," said Tom Haueter, an aviation safety expert. "Certainly one aspect of turning it off is because you don't want to be seen."
Also Friday, seismologists at a Chinese university say monitors captured "seismic events" on the sea floor along the plane's original flight path.
"Judging from the time and location of the two events, the sea floor event may have been caused by MH370 crashing into the sea," the seismologists said in a statement.
The Wall Street Journal first reported Thursday the engines continued to transmit data after the plane vanished from radar.
Officials have told CBS News the plane had enough fuel to carry it out to the west into the Indian Ocean, so the search is growing even larger. While they believe it likely crashed in water, it's also possible it landed somewhere.
Malaysian Transport Minister Hishammuddin Hussein said the search was expanding further afield into the eastern stretches of the South China Sea and on the western side of the Malay Peninsula, northwest into the Andaman Sea and further into the India Ocean.
The Beijing-bound flight last communicated with air traffic base stations east of Malaysia in the South China Sea, which initially was the focus of the search. The theory that the plane turned back and flew west has been strengthened because Malaysia says it has military radar records showing unidentified blips that could indicate the plane doing this.
"I will be the most happiest person if we can actually confirm that it is the MH370, then we can move all assets from the South China Sea to the Strait of Malacca," Hishammuddin said.
India said it was searching hundreds of small, uninhabited islands in the Andaman Sea more than 745 miles to the west of the plane's last known position. Spokesman Col. Harmit Singh of India's Tri-Services Command said it began land searches after sweeping seas to the north, east and south of the Andaman and Nicobar Islands.
Malaysian officials declined to discuss when -- or even whether -- they had information about signals to satellites, and said they would release details only when they were verified.
"I hope within a couple of days to have something conclusive," Hishammuddin told a news conference.
A team of five U.S. officials with air traffic control and radar expertise -- three from the U.S. National Transportation Safety Board and two from the Federal Aviation Administration -- has been in Kuala Lumpur since Monday to assist Malaysia with the investigation.
If the plane had disintegrated during flight or suffered some other catastrophic failure, all signals -- pings to satellites, data messages and the transponder -- would be expected to stop at the same time.
No theory, however, has been ruled out in one of modern aviation's most puzzling mysteries. Investigators are also probing the backgrounds of the two men in the cockpit, Aiello reported. The pilots, ages 53 and 27, are described by family as steady and stable.
Meanwhile, it's an anguished time for the families of the passengers and crew, Aiello reported. A wall at the Malaysian airport where the flight originated is covered with hundreds of messages of hope, including one that says "sister and father are missing, please come back."
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