The number of countries aiding the massive international search for Malaysia Airlines Flight 370 swelled to 26 on Monday as Malaysia's defense minister held out thin hope that the 239 people aboard the missing Boeing 777 will be found alive.
Malaysian Defense Minister Hishammuddin Hussein said that, 10 days into the investigation, nothing had been ruled out, including hijacking, sabotage, pilot suicide or mass murder.
"The fact that there was no distress signal, no ransom notes, no parties claiming responsibility, there is always hope," Hishammuddin said.
The unprecedented hunt is taking place as preliminary investigations revealed that the plane's co-pilot apparently spoke the last words to air-traffic controllers.
Malaysia Airlines CEO Ahmad Jauhari Yahya said the co-pilot of the plane was probably the person who calmly said, "All right, good night."
Officials previously have said that those words came at a point in the March 8 flight when one of the jet's data communications systems already had been switched off. Ahmad, however, said Monday that the last communication from the system came minutes before the words were spoken, but that it was not clear if the system was turned off before or after the words were spoken.
The timing of the last words sharpened suspicions that one or both of the pilots may have been involved in the plane's disappearance.
The development comes as the search-and-rescue mission has been extended to what officials are calling two "corridors" that the plane may have flown from its last known position. One is an arc north toward central Asia, the other is an arc south toward the southern Indian Ocean and Australia.
Australian Prime Minister Tony Abbott told parliament that he agreed to take the lead scouring the southern Indian Ocean for the "ill-fated aircraft" during a conversation Monday with Malaysia's leader.
"Australia will do its duty in this matter," Abbott told parliament. "We will do our duty to the families (of the 227 passengers and 12 crewmembers) on that aircraft who are still absolutely devastated by their absence, and who are still profoundly, profoundly saddened by this as yet unfathomed mystery."
Contributing: John Bacon; Associated Press