Story highlights Official: Programmed change in direction occurred 12 minutes before sign off

Analyst: "Sometimes an erratic flight path is heroism, not terrorism"

Law enforcement official: Plane's turn almost certainly programmed from cockpit

Officials say nothing on pilots' computers, e-mails indicates deviation was planned

New information from the Thai government bolsters the belief that missing Malaysia Airlines Flight 370 took a sharp westward turn after communication was lost.

And it looks like that turn was no accident.

A law enforcement official told CNN Tuesday that the aircraft's first turn to the west was almost certainly programmed by somebody in the cockpit.

The official, who has been briefed on the investigation, said the programmed change in direction was entered at least 12 minutes before the plane's co-pilot signed off to air traffic controllers, telling them, "All right, good night."

Analysts on CNN's "AC360" offered different interpretations of what that could mean -- with some experts cautioning the change in direction could have been part of an alternate flight plan programmed in advance in case of emergency, and others warning it could show something more nefarious was afoot.

"We don't know when specifically it was entered," said Mary Schiavo, a CNN aviation analyst and former inspector general for the U.S. Department of Transportation.

New York Times reporter Michael Schmidt said the new timeframe "makes the issue of foul play seem more significant."

"Because by doing that," he said, "what it basically shows is that this thing was already heading in a different direction when they're saying good night."

But still, the new details about what happened don't add up to a clear answer.

"Like everything on this story, we learn a little bit," Schmidt said, "but then we just have more questions."

Evidence that someone programmed the plane's computer and the Thai data that surfaced Tuesday corroborate a leading theory from Malaysian investigators: The missing plane veered off course in a deliberate act by someone who knew what they were doing.

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Photos: The search for MH370 Photos: The search for MH370 Two years after Malaysia Airlines Flight 370 went missing, a relative of one of the passengers burns incense in Beijing on March 8, 2016. Flight 370 vanished on March 8, 2014, as it flew from Kuala Lumpur, Malaysia, to Beijing. There were 239 people on board. Hide Caption 1 of 43 Photos: The search for MH370 On July 29, police carry a piece of debris on Reunion Island, a French territory in the Indian Ocean. A week later, authorities confirmed that the debris was from the missing flight. Hide Caption 2 of 43 Photos: The search for MH370 Staff members with the Australian Transport Safety Bureau examine a piece of aircraft debris at their laboratory in Canberra, Australia, on July 20. The flap was found in June by residents on Pemba Island off the coast of Tanzania, and officials had said it was highly likely to have come from Flight 370. Experts at the Australian Transport Safety Bureau, which is heading up the search for the plane, confirmed that the part was indeed from the missing aircraft. Hide Caption 3 of 43 Photos: The search for MH370 In late February, American tourist Blaine Gibson found a piece of plane debris off Mozambique, a discovery that renewed hope of solving the mystery of the missing flight. The piece measured 35 inches by 22 inches. A U.S. official said it was likely the wreckage came from a Boeing 777, which MH370 was. Hide Caption 4 of 43 Photos: The search for MH370 Relatives of the flight's passengers console each other outside the Malaysia Airlines office in Subang, Malaysia, on February 12, 2015. Protesters had demanded that the airline withdraw the statement that all 239 people aboard the plane were dead. Hide Caption 5 of 43 Photos: The search for MH370 A police officer watches a couple cry outside the airline's office building in Beijing after officials refused to meet with them on June 11, 2014. The couple's son was on the plane. Hide Caption 6 of 43 Photos: The search for MH370 Members of the media scramble to speak with Azharuddin Abdul Rahman, director general of Malaysia's Civil Aviation Department, at a hotel in Kuala Lumpur, Malaysia, on May 27, 2014. Data from communications between satellites and the missing flight was released the day before, more than two months after relatives of passengers said they requested it be made public. Hide Caption 7 of 43 Photos: The search for MH370 Operators aboard the Australian ship Ocean Shield move Bluefin-21, the U.S. Navy's autonomous underwater vehicle, into position to search for the jet on April 14, 2014. Hide Caption 8 of 43 Photos: The search for MH370 A member of the Royal New Zealand Air Force looks out of a window while searching for debris off the coast of western Australia on April 13, 2014. Hide Caption 9 of 43 Photos: The search for MH370 The HMS Echo, a vessel with the British Roya; Navy, moves through the waters of the southern Indian Ocean on April 12, 2014. Hide Caption 10 of 43 Photos: The search for MH370 A Royal Australian Air Force AP-3C Orion, on a mission to drop sonar buoys to assist in the search, flies past the Australian vessel Ocean Shield on April 9, 2014. Hide Caption 11 of 43 Photos: The search for MH370 A relative of a missing passenger cries at a vigil in Beijing on April 8, 2014. Hide Caption 12 of 43 Photos: The search for MH370 Australian Defense Force divers scan the water for debris in the southern Indian Ocean on April 7, 2014. Hide Caption 13 of 43 Photos: The search for MH370 A towed pinger locator is readied to be deployed off the deck of the Australian vessel Ocean Shield on April 7, 2014. Hide Caption 14 of 43 Photos: The search for MH370 A member of the Royal New Zealand Air Force looks at a flare in the Indian Ocean during search operations on April 4, 2014. Hide Caption 15 of 43 Photos: The search for MH370 On March 30, 2014, a woman in Kuala Lumpur prepares for an event in honor of those aboard Flight 370. Hide Caption 16 of 43 Photos: The search for MH370 The sole representative for the families of Flight 370 passengers leaves a conference at a Beijing hotel on March 28, 2014, after other relatives left en masse to protest the Malaysian government's response to their questions. Hide Caption 17 of 43 Photos: The search for MH370 A member of the Royal Australian Air Force is silhouetted against the southern Indian Ocean during the search for the missing jet on March 27, 2014. Hide Caption 18 of 43 Photos: The search for MH370 Flight Lt. Jayson Nichols looks at a map aboard a Royal Australian Air Force aircraft during a search on March 27, 2014. Hide Caption 19 of 43 Photos: The search for MH370 People in Kuala Lumpur light candles during a ceremony held for the missing flight's passengers on March 27, 2014. Hide Caption 20 of 43 Photos: The search for MH370 Malaysian Prime Minister Najib Razak, center, delivers a statement about the flight on March 24, 2014. Razak's announcement came after the airline sent a text message to relatives saying it "deeply regrets that we have to assume beyond any reasonable doubt that MH 370 has been lost and that none of those onboard survived." Hide Caption 21 of 43 Photos: The search for MH370 Grieving relatives of missing passengers leave a hotel in Beijing on March 24, 2014. Hide Caption 22 of 43 Photos: The search for MH370 A passenger views a weather map in the departures terminal of Kuala Lumpur International Airport on March 22, 2014. Hide Caption 23 of 43 Photos: The search for MH370 A Chinese satellite captured this image, released on March 22, 2014, of a floating object in the Indian Ocean, according to China's State Administration of Science. It was a possible lead in the search for the missing plane. Surveillance planes were looking for two objects spotted by satellite imagery in remote, treacherous waters more than 1,400 miles from the west coast of Australia. Hide Caption 24 of 43 Photos: The search for MH370 Satellite imagery provided by the Australian Maritime Safety Authority on March 20, 2014, showed debris in the southern Indian Ocean that could have been from Flight 370. The announcement by Australian officials raised hopes of a breakthrough in the frustrating search. Hide Caption 25 of 43 Photos: The search for MH370 Another satellite shot provided by the Australian Maritime Safety Authority shows possible debris from the flight. Hide Caption 26 of 43 Photos: The search for MH370 A distraught relative of a missing passenger breaks down while talking to reporters at Kuala Lumpur International Airport on March 19, 2014. Hide Caption 27 of 43 Photos: The search for MH370 On March 18, 2014, a relative of a missing passenger tells reporters in Beijing about a hunger strike to protest authorities' handling of information about the missing jet. Hide Caption 28 of 43 Photos: The search for MH370 U.S. Navy crew members assist in search-and-rescue operations in the Indian Ocean on March 16, 2014. Hide Caption 29 of 43 Photos: The search for MH370 Members of the Chinese navy continue search operations on March 13, 2014. After starting in the sea between Malaysia and Vietnam, the plane's last confirmed location, search efforts expanded west into the Indian Ocean. Hide Caption 30 of 43 Photos: The search for MH370 A Vietnamese military official looks out an aircraft window during search operations March 13, 2014. Hide Caption 31 of 43 Photos: The search for MH370 Malaysian air force members look for debris near Kuala Lumpur on March 13, 2014. Hide Caption 32 of 43 Photos: The search for MH370 Relatives of missing passengers wait for the latest news at a hotel in Beijing on March 12, 2014. Hide Caption 33 of 43 Photos: The search for MH370 A member of the Vietnamese air force checks a map while searching for the missing plane on March 11, 2014. Hide Caption 34 of 43 Photos: The search for MH370 A Vietnamese air force plane found traces of oil that authorities had suspected to be from the missing Malaysia Airlines plane, the Vietnamese government online newspaper reported on March 8, 2014. However, a sample from the slick showed it was bunker oil, typically used to power large cargo ships, Malaysia's state news agency, Bernama, reported on March 10, 2014. Hide Caption 35 of 43 Photos: The search for MH370 A U.S. Navy Seahawk helicopter lands aboard the USS Pinckney to change crews on March 9, 2014, before returning to search for the missing plane in the Gulf of Thailand. Hide Caption 36 of 43 Photos: The search for MH370 Buddhist monks at Kuala Lumpur International Airport offer a special prayer for the missing passengers on March 9, 2014. Hide Caption 37 of 43 Photos: The search for MH370 Members of a Chinese emergency response team board a rescue vessel at the port of Sanya in China's Hainan province on March 9, 2014. Hide Caption 38 of 43 Photos: The search for MH370 The rescue vessel sets out from Sanya in the South China Sea on March 9, 2014. Hide Caption 39 of 43 Photos: The search for MH370 Malaysian Prime Minister Najib Razak, center, arrives to meet family members of missing passengers at the reception center at Kuala Lumpur International Airport on March 8, 2014. Hide Caption 40 of 43 Photos: The search for MH370 A relative of two missing passengers reacts at their home in Kuala Lumpur on March 8, 2014. Hide Caption 41 of 43 Photos: The search for MH370 Chinese police at the Beijing airport stand beside the arrival board showing delayed Flight 370 in red on March 8, 2014. Hide Caption 42 of 43 Photos: The search for MH370 Malaysia Airlines Group CEO Ahmad Juahari Yahya, front, speaks during a news conference at a hotel in Sepang on March 8, 2014. "We deeply regret that we have lost all contacts" with the jet, he said. Hide Caption 43 of 43

But investigators still don't know who was at the controls, or why whoever was flying the plane apparently took it far from its original destination.

An initial search of the pilots' personal computers and e-mails found nothing to indicate that the sudden deviation in the aircraft's route was planned, U.S. officials said Tuesday after being briefed by Malaysian authorities.

The officials said they had also reviewed cockpit conversations between the plane and air traffic controllers and heard nothing suspicious or anything that would explain why the jetliner changed course.

And a flight simulator belonging to pilot Zaharie Ahmad Shah did not show any of the unexplained paths the plane may have flown after it went off the grid, officials said.

Schiavo said it's no surprise investigators found nothing suspicious in the pilots' homes.

"I've worked on many cases were the pilots were suspect, and it turned out to be a mechanical and horrible problem," she said. "And I have a saying myself: Sometimes an erratic flight path is heroism, not terrorism. And I always remind myself of that, not to jump to that conclusion. Sometimes pilots are fighting amazing battles, and we never hear about it. "

Thailand: Plane sent intermittent signal

The Thai military's revelation that it also spotted the plane turning west toward the Strait of Malacca is one encouraging sign that investigators could be on the right track after days of searching for the missing plane have failed to turn up any answers about its location.

The Thai military was receiving normal flight path and communication data from the Boeing 777-200 on its planned March 8 route from Kuala Lumpur to Beijing until 1:22 a.m., when it disappeared from its radar.

Six minutes later, the Thai military detected an unknown signal, a Royal Thai Air Force spokesman told CNN. This unknown aircraft, possibly Flight 370, was heading the opposite direction.

Malaysia says the evidence suggests that the plane was deliberately flown off-course, turning west and traveling back over the Malay Peninsula and out into the Indian Ocean.

The Thai data are the second radar evidence that the plane did indeed turn around toward the Strait of Malacca.

It follows information from the Malaysian air force that its military radar tracked the plane as it passed over the small island of Pulau Perak in the Strait of Malacca.

"The unknown aircraft's signal was sending out intermittently, on and off and on and off," the spokesman said. The Thai military lost the unknown aircraft's signal because of the limits of its military radar, he said.

Investigators say they're still not sure where the plane ended up.

The latest findings say the plane's last known location detected by a satellite is along two wide arcs: one stretching north over Asia and the other south into the Indian Ocean. The plane's last electronic connection with the satellite was about six hours after it last showed up on Malaysian military radar.

The total area now being searched stands at 2.97 million square miles -- an area nearly the size of the continental United States -- Hishammuddin Hussein, the Malaysian defense and transport minister said.

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"This is an enormous search area," Hishammuddin said. "And it is something that Malaysia cannot possibly search on its own. I am therefore very pleased that so many countries have come forward to offer assistance and support to the search and rescue operation."

Turn made by computer?

The pilot and first officer of the missing plane, both of them Malaysian, have come under particular scrutiny in the search for clues.

But officials have reported no evidence to tie the pilot and first officer to the plane's disappearance.

One aviation expert, writing an opinion piece for CNN.com , floated the idea last week that whoever changed the plane's course was an expert.

The cockpit computer programming analysis, first reported by The New York Times Tuesday, has increased investigators' focus on the pilot and first officer, the newspaper said.

Asked about the report Tuesday, Malaysia Airlines Chief Executive Ahmad Jauhari Yahya said, "As far as we're concerned, the aircraft was programmed to fly to Beijing. That's the standard procedure."

But he didn't rule out the possibility the flight path had been reprogrammed.

"Once you're in the aircraft," he said, "anything is possible."

China clears citizens

China says it has found no evidence that any of its citizens on board the missing plane were involved in hijacking or terrorism.

Background checks on all passengers from the Chinese mainland on the plane have found nothing to support such suspicions, Huang Huikang, the Chinese ambassador to Malaysia, said Tuesday, according to the state-run Chinese news agency Xinhua.

Authorities have said they are investigating all 239 people who were on board the flight, which disappeared more than 10 days ago.

According to the airline, 153 of the 227 passengers on board the plane came from mainland China or Hong Kong.

By effectively ruling out suspicions for a large majority of the passengers, Chinese authorities appear to have significantly shortened the list of possible suspects in the investigation.

The Chinese ambassador's statement is also likely to greatly dampen speculation that Uyghur separatists from China's far western region of Xinjiang might have been involved in the plane's disappearance.

One of the two long corridors where authorities say the plane was last detected stretched over Xinjiang, and unconfirmed reports had suggested the possibility that Uyghurs might be connected to the case.

Chinese authorities have accused separatists from Xinjiang of carrying out a terrorist attack this month in which eight attackers armed with long knives stormed a train station in Kunming, a city in southwestern China, killing 29 people and wounding more than 140.

China said Tuesday that it had begun to search for the plane in the parts of its territory that fall under the northern corridor, deploying satellite and radar resources.

Experts are analyzing past and present data along the arc stretching through Chinese territory, Hong Lei, a Foreign Ministry spokesman, said at a news briefing Tuesday in Beijing.

Still a mystery

Eleven days after Flight 370 disappeared, the bottom line is that the fate of the flight remains a mystery. As time has passed, initial theories about mechanical error have led to more elaborate ideas about complicated hijacking or commandeering plots.

Former Malaysia Airlines pilot Nik Huzlan has flown the same aircraft that is now missing.

"I know, I flew this plane," he said. "This is very, very strange. The lack of communication is puzzling. How the pilots are not communicating."

Huzlan has come up with his own theories.

"From (the) second or third day, I've come to my own private conclusion that it must have been unlawful human interference," he said. "It could have been anyone on the airplane."

CNN has talked to more than half a dozen U.S. military and intelligence officials who emphasize that while no one knows what happened to the plane, it is more logical to conclude it crashed into the Indian Ocean.

The officials say there is no evidence that any U.S. satellite data registered an unknown aircraft in any of the Asian countries along the path the plane may have taken. According to these officials, it is overwhelmingly likely if the plane had crashed on land, there would be some evidence of that, and if it had landed, someone would have seen it.

U.S. Defense Secretary Chuck Hagel raised the issue of transparency when he spoke with his Malaysian counterpart Monday, according to two U.S. officials.

Both officials said it was not a criticism of the Malaysians, but more a discussion about the need to share information with the world on one of the most complex search operations in history.

"He was saying the best way to handle this is to continue to be transparent and tell what you know when you know it," one official said of Hagel's conversation. In the first days after the incident, some U.S. officials had said the Malaysian government did not share enough radar and technical data about the flight.