Malaysia Airlines Flight 370: Where the investigation stands now

Malaysian authorities have not ruled out any possible explanation for what happened to Malaysia Airlines Flight 370, but have said the evidence so far suggests it was deliberately turned back across Malaysia to the Strait of Malacca, with its communications systems disabled. They are unsure what happened next.

Police are considering possibilities including hijacking, sabotage, terrorism or issues related to the mental health of the pilots or anyone else on board.

CBS News rounds up the latest on where the investigation stands now.

Follow the latest updates on the search here. Find more information about the 239 people on board here. And for complete, ongoing coverage, visit our special section: Malaysia Airlines Flight 370.

FBI assisting investigation - The FBI is assisting the Malaysian government in reading the flight simulator confiscated at the home of the plane's captain, Zaharie Ahmad Shah. Malaysian officials said they were trying to restore files which they said were deleted last month.

CBS News learned the hard drive of the flight simulator is at the FBI lab in Quantico, Virginia, where analysts were said on March 26 to be in the final stages of analyzing it.

The FBI was able to recover some of the deleted files, but sources told CBS News nothing had emerged to raise any suspicions thus far. Nor did investigators find anything on the two pilots' personal computers to be particularly significant to the investigation, the sources said.

In Kuala Lumpur, a senior Malaysian law enforcement official told CBS News on March 27 that, at this point in the investigation, there was no tangible evidence connecting any individual (including either of the pilots) with the crash of Flight 370. While the official said any reporting suggesting fault on the part of either pilot would be "speculation."

Files deleted from flight simulator - According to Malaysian officials, the files containing records of simulations carried out on the program were deleted Feb. 3 from the elaborate flight simulator found in Zaharie's home. It was not immediately clear whether investigators thought that deleting the files was unusual. Citing a senior police officer with direct knowledge of the investigation, Reuters reported that the simulator included programs for runways in the Maldives, Sri Lanka and other Indian Ocean countries, as well as runways in the U.S. and Europe.

Practicing on different kinds of runways would not be unusual, CBS News national security analyst Juan Zarate said. But, he added, authorities will have to check what those runways look like to see if they "match with runways in the region and perhaps some smaller runways in the Indian Ocean that could give them some clues as to where to look."

Zaharie had previously posted photos online of the simulator, which was made with three large computer monitors and other accessories.

Course change programmed into flight computer - Sources told CBS News that there's evidence Malaysia Airlines Flight 370 turned off its route when someone typed a course change into a cockpit navigation computer called the flight management system, which would require training in the Boeing 777 systems. But sources say checks of the pilots' email and computers turned up nothing to suggest a plot.

"All right, good night" - Malaysia Airlines CEO Ahmad Jauhari Yahya said Monday that "initial investigations show it was the co-pilot who spoke" those final words from the cockpit to air traffic control. But government officials did not say the speaker's identity had been confirmed. Officials also revised the timeline for that final message, suggesting that it may have come shortly before the flight's Aircraft and Communications Addressing and Reporting System, or ACARS, was shut off, rather than after.

Pilots' homes raided - Malaysian police searched the homes of both pilot, Zaharie, and the co-pilot, Fariq Abdul Hamid, Saturday. Whoever disabled the plane's communication systems and then flew the jet must have had a high degree of technical knowledge and flying experience, Malaysian officials and aviation experts said, adding to suspicions that one or both of the pilots may have been involved in the disappearance of the flight.

Passengers and crew investigated - Malaysian officials said Wednesday that requested background checks had been received for all foreign passengers except those from Ukraine and Russia - which account for three passengers. China said background checks of the 154 Chinese citizens on board turned up no links to terrorism, apparently ruling out the possibility that Uighur Muslim militants who have been blamed for terror attacks within China might have been involved in the disappearance. Malaysian officials said Wednesday that the requested background checks

CBS News' Seth Doane reported Monday that investigators were also paying close attention to one of the passengers who was a flight engineer for a private aviation charter company. He was believed to be heading for Beijing to check on one of his company's charter aircraft.

Malaysian police were also looking into the engineers and ground staff who may have had contact with the plane before it took off.

FBI formally joins investigation - A U.S. official, speaking on condition of anonymity because the official was not authorized to discuss the ongoing investigation by name, said the FBI has been provided electronic data to analyze. U.S. Attorney General Eric Holder said Wednesday U.S. investigators are prepared to help any way they can.

While the FBI had sent representatives to Malaysia and offered to help with the investigation, the Americans had not been invited to participate in the Malaysian-led probe, CBS News' Bob Orr reports. "It's a Malaysian airline flight that was lost, but we are assisting, as are many other nations, in every way that we can," White House Press Secretary Jay Carney told reporters Friday.

"You have to look at everything" - Investigators must check out every possible explanation, ranging from terrorism to pilot suicide to cargo theft or smuggling, said Ken Maxwell, one of the principal investigators of the TWA 800 and Egypt Air 990 flight disasters. In an interview with CBS News, Maxwell said that the scope of the criminal investigation "will be extremely broad," and that investigators have to consider, "What's in the cargo? Who's on that plane? Who would have motive or intent to utilize that aircraft?"