"In view of this latest development, the Malaysian authorities have refocused their investigation into the crew and passengers on board," Najib told reporters, reading from a written statement but not taking any questions.
Police on Saturday went to the Kuala Lumpur homes of both the pilot and co-pilot of the missing plane, according to a guard and several local reporters. Authorities have said they will investigate the pilots as part of their probe, but have released no information about how they are progressing.
Experts have previously said that whoever disabled the plane's communication systems and then flew the jet must have had a high degree of technical knowledge and flying experience. One possibility they have raised was that one of the pilots wanted to commit suicide.
The plane was carrying 239 people when it departed for an overnight flight from Kuala Lumpur to Beijing at 12:40 a.m. on March 8. Its communications with civilian air controllers were severed at about 1:20 a.m., and the jet went missing -- heralding one of the most puzzling mysteries in modern aviation history.