The FBI is formally joining the investigation into the missing Malaysian airliner and is expected to begin analyzing hard drives from computers seized at the pilots' homes as soon as this week.

A federal law enforcement official said the material, including a flight simulator recovered from one of the pilot's homes, is likely to be shipped to the FBI's lab in Quantico, Va. The official is not authorized to speak publicly about the investigation and requested anonymity.

Since the plane's disappearance, the FBI and Justice Department had offered to assist the Malaysian government but until now had not been formally invited to join the inquiry as is required.

Attorney General Eric Holder said Wednesday that the two governments have been "in ongoing conversations about how we can help."

"We're working with authorities, but we don't have any theories (on the cause of the plane's disappearance)," Holder said Wednesday.

In Malaysia, investigators said Wednesday they are trying to restore files deleted last month from the home flight simulator of the pilot of a missing Malaysian plane, but the wait for answers was too much for some relatives who disrupted a news conference....