Sources: Co-pilot spoke last words from cockpit

The co-pilot of the missing Malaysian jetliner spoke the last words heard from the cockpit, the airline's CEO said on Monday, as investigators consider suicide by the captain or first officer as one possible explanation for the disappearance.

No trace of Beijing-bound Malaysia Airlines Flight MH370 has been found since it vanished on March 8 with 239 people aboard. Investigators are increasingly convinced it was divertedmiles off course by someone with deep knowledge of the Boeing 777 and commercial navigation.

A search unprecedented in its scale is now under way for the plane, stretching from the Caspian Sea in the north to deep in the southern Indian Ocean.

Airline CEO Ahmad Jauhari Yahya also said it was unclear exactly when one of the plane's automatic tracking systems had been disabled.

Suspicions of hijacking or sabotage had hardened further when officials said on Sunday that the last radio message from the plane -- an informal "all right, good night" -- was spoken after the ACARS system, a maintenance computer that relays data on the plane's status, was shut down.

"Initial investigations indicate it was the co-pilot [Fariq Ab Hamid] who basically spoke the last time it was recorded on tape," Ahmad Jauhari said yesterday. It was a signoff to air traffic controllers at 1:19 a.m. The last ACARS transmission was received at 1:07 a.m.