WASHINGTON -- A review of the emails and a search of a home flight simulator have found nothing so far to suggest the pilots on the missing plane purposely compromised the flight by diverting it away from Beijing, according to two U.S. law enforcement officials.
"Nothing stuck out," said one of the sources, who was briefed on the search conducted by Malaysian officials.
He said authorities sought to find out whether the pilot, Zaharie Ahmad Shah, might have been training on the simulator, specifically how to turn off the transponders and other in-flight devices before the March 8 flight. And they examined whether he had practiced flight patterns taking him away from Beijing, the aircraft's intended destination after leaving Kuala Lumpur, Malaysia's capital.
But, the source said, investigators "didn't find that."
He added that authorities have discovered nothing particularly disturbing in the pilots' personal lives. The copilot, in fact, was preparing for his wedding, the source said.
The U.S. sources also said they have learned that conversations between the cockpit and the air traffic control tower in Malaysia were friendly, routine and professional, with no hint of impending trouble.
The developments Tuesday appeared to weaken theories of a suicide, leaving U.S. law enforcement officials to focus on hijack scenarios or other sabotage, including whether someone preprogrammed some of the aircraft's computer systems to execute the diversion.
"It's still possible that someone entered the cockpit and took the flight a different direction," said one U.S. source, speaking confidentially because the probe is ongoing. "Or it was tinkered with beforehand."
A third theory remains that one of the pilots "took it upon himself" to divert the plane for unknown reasons.
Federal officials in Washington also discounted any terrorist link to a shoe-bomb plot that once was being prepared in Malaysia to follow the Sept. 11, 2001, terrorist attacks in the United States.
Details of that plot resurfaced last week when Saajid Badat testified in the New York trial of Osama bin Laden's son-in-law, Sulaiman abu Ghaith, and recalled how Al Qaeda had tasked him to board a flight with a bomb in his shoes. But Badat said he decided not to follow through.
The U.S. officials said that in the last few days, Malaysian officials have been more open in sharing their information and asking for help from the United States with investigative and technological expertise.
China's role in the search also appeared to grow Tuesday. The official New China News Agency said two naval groups turned attention westward, to the Indian Ocean. One fleet is headed through the Malacca Strait into waters west of the Andaman Islands, the report said. Another fleet was heading for waters southwest of Sumatra, an island in western Indonesia.
U.S. law enforcement officials have expressed frustration about the course of the investigation being run by the Malaysian officials, and the fact that authorities there have often contradicted themselves about various matters in the investigation.
"They're not talking much, and they should ask us for more help," said the second source. "I'm not saying these people are not trustworthy. It's that nobody knows at this point much more than we did at the start."
He said U.S. officials believe the plane eventually crashed into water. "As we get further into this, the percentages rest in the ocean," he said. "You have to believe the plane crashed into the ocean."
In addition, a team of investigators from the U.S. National Transportation Safety Board has been dispatched to Kuala Lumpur. That team is headed by John Lovell, a longtime NTSB investigator with experience in assisting foreign governments with crash investigations.
In 2011, Lovell led a team of NTSB and Federal Aviation Administration experts in South Korea to help investigate the crash of Asiana flight 991, a Boeing 747-400F cargo plane that crashed into the East China Sea after an in-flight fire.
In 2008, Lovell led the American team sent to Madrid to help determine how Spanair Flight 5022, a McDonnell Douglas MD-82 bound for Las Palmas in the Canary Islands, crashed during takeoff. Of the 172 passengers and crew on board, 146 were killed in the crash and subsequent fire.