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KUALA LUMPUR, Malaysia (CBSNews.com)- When someone at the controls calmly said the last words heard fromthe missing Malaysian jetliner,one of the Boeing 777's communications systems had already been disabled, authorities said Sunday, adding to suspicions that one or both of the pilots were involved in disappearance of the flight.

Investigators also examined a flight simulator confiscated from the home of one of the pilots and dug through the background of all 239 people on board, as well as the ground crew that serviced the plane.

The Malaysia Airlines jet took off from Kuala Lumpur in the wee hours of March 8, headed to Beijing. On Saturday, the Malaysian government announced findings that strongly suggested the plane was deliberately diverted and may have flown as far north as Central Asia or south into the vast reaches of the Indian Ocean.

Authorities have saidsomeone on board the planefirst disabled one of its communications systems - the Aircraft and Communications Addressing and Reporting System, or ACARS - about 40 minutes after takeoff. The ACARS equipment sends information about the jet's engines and other data to the airline.

Around 14 minutes later, the transponder that identifies the plane to commercial radar systems was also shut down. The fact that both systems went dark separately offered strong evidence that the plane's disappearance was deliberate.

On Sunday, Malaysian Defense Minister Hishammuddin Hussein said at a news conference that that the final, reassuring words from the cockpit - "All right, good night" - were spoken to air traffic controllers after the ACARS system was shut off. Whoever spoke did not mention any trouble on board.

Air force Maj. Gen. Affendi Buang told reporters he did not know whether it was the pilot or co-pilot who spoke to air traffic controllers.

Given the expanse of land and water that might need to be searched, finding the wreckage could take months or longer. Or it might never be located. Establishing what happened with any degree of certainty will probably require evidence from cockpit voice recordings and the plane's flight-data recorders.

The search area now includes 11 countries the plane might have flown over, Hishammuddin said, adding that the number of countries involved in the operation had increased from 14 to 25.

"The search was already a highly complex, multinational effort," he said. "It has now become even more difficult."

The search effort initially focused on the relatively shallow waters of the South China Sea and the Strait of Malacca, where the plane was first thought to be. Hishammuddin said he had asked governments to hand over sensitive radar and satellite data to try to get a better idea of the plane's final movements.

With more information, he said, the search zone could be narrowed "to an area that is more feasible."

Malaysia is leading the search for the plane and the investigation into its disappearance.

© 2014 CBS Interactive Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.

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