As the investigation into the mysterious disappearance of Malaysia Airlines Flight 370 focused Wednesday on deleted files from the home flight simulator of the pilot, Capt. Zaharie Ahmad Shah, a host of possible explanations — and conspiracy theories — have materialized.

Evidence thus far suggests the Boeing 777, which took off on March 8 carrying 239 people on a flight from Kuala Lumpur to Beijing, was deliberately turned back across Malaysia with its communications systems disabled. Exactly what occurred next — and why — remains a mystery.

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“Nothing is going to be determined as a fact until we either have a wreckage or an airplane,” aviation expert Al Yurman told FoxNews.com. “You cannot make factual statements in an aircraft accident until you have either of those. What’s happening now is complete speculation; everything’s possible.”

Yurman, a former National Transportation Safety Board investigator, said he suspected some kind of criminal activity behind the incident. Shah, the plane’s 53-year-old pilot who has more than 18,000 hours of flight experience, reportedly deleted files containing records of simulations on Feb. 3 and co-pilot Fariq Abdul Hamid has previously allowed unauthorized people into cockpits, Yurman noted.

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“So my first thought was to look into them and their backgrounds,” he said. “We also had at least two Iranians with false passports. I think they have to look into that more as well.”

Investigators poring through Shah’s home flight simulator are likely searching for information related to remote airports where he may have previously practiced landings, Yurman said.

Scott Shankland, an American Airlines pilot with experience on Boeing 777s, told The Associated Press that a captain would know how to disable the plane’s tracking systems, but said a hijacker would likely be “hunting and pecking” for quite a while.

“'Do I pull this switch? Do I pull that?’ You could disable a great deal” of the tracking equipment, Shankland said, “but possibly not all of it.”

John Hansman, an aeronautics professor at MIT, said it’s possible an intruder turned off the plane’s transponders, but added that knowing how to completely shut down other systems and ultimately make a successful, hidden landing would be much more difficult.

“If it was a hijacking, it was probably a hijacking gone bad,” said Hansman, who told The Associated Press he believes a series of malfunctions or even a cabin fire could have incapacitated the pilots, much like the 1999 crash in South Dakota that killed golfer Payne Stewart and five others.

Yurman, who investigated that 1999 crash while with the NTSB, quickly discounted that possibility, saying any serious issue with the aircraft would have led to several emergency alerts and a wide field of debris upon any crash.

“If there was a malfunction where the airplane couldn’t fly anymore, you’d ultimately have debris, you’d have a crew giving a mayday, issuing several alerts to get help,” Yurman said. “And some of that debris will be seen or show up on land or on water somewhere. The debris field, plus its oil slicks, would be out there more than likely for a long time.”

So what happened to Flight 370 and why can’t investigators find it?

To Yurman, citing the facts that no wreckage has been found and questions circulating on the crew’s background, the aircraft is “more than likely” at a remote site to be reused at a later date. If that’s the case, Yurman said the plane would be repainted, given new identifying characteristics and be prepared to fly as a new entity.

“If it was a hijacking, then it was well planned,” he said. “You had to get the right people onto the flight, it had to be planned in advance, they had to know what they’re going to do with it and where to go.”

Other theories as to what happened to Flight 370 include that it flew in another aircraft’s shadow to avoid detection by appearing as a single blip on radar screens. Aviation blogger Keith Ledgerwood wrote he believes the aircraft “snuck out” of the Bay of Bengal by using Singapore Airlines Flight 68 as cover. Yet another theory asserts that the plane could have cracked its lap joints, leading to sudden depressurization and knocking the pilots unconscious.

John Cane, an aviation expert and retired Marine, told FoxNews.com he believes a “criminal act” led to the plane’s disappearance, but stopped short of saying it was likely hijacked to be used later, perhaps as a weapon of mass destruction

“The reason I don’t lean toward it being hijacked and then landed in a foreign country to be used later is that you’ve already advertised that there’s a missing aircraft out there now,” Cane said. “Why would you allow your potential targets to raise their defenses? That’s not the way terrorists operate.”

When pressed to give the likeliest location of the plane more than 10 days after it disappeared, Cane said Flight 370 was either in an ocean or a jungle.

“And in those two possibilities, it’s like finding a needle in a haystack,” Cane told FoxNews.com. “But at this point, we can’t take anything off the table.”

The Associated Press contributed to this report.