Malaysia's national police chief says all 227 passengers aboard the jet airliner that disappeared last month have been cleared of wrongdoing, but authorities are continuing to investigate the two pilots and other crew members.
Inspector General Khalid Abu Bakar said Wednesday investigators need more time to try to determine why Malaysia Airlines Flight 370 vanished 25 days ago on a flight from Kuala Lumpur to Beijing.
The police chief said the investigation "may go on and on and on," and it is possible that there may never be any complete answers to the mystery of the Boeing 777 jet that vanished.
An international search for debris in the southern Indian Ocean and a criminal investigation by Malaysian police have so far proven fruitless.
U.S. Defense Secretary Chuck Hagel says Southeast Asian defense ministers meeting in Hawaii later this week will certainly discuss the incident. Without criticizing Malaysia's handling of the search for the plane, he said there are "always lessons to be learned" from such a crisis.
The police inspector general in Kuala Lumpur said the possibilities police are considering include hijacking, sabotage and personal or psychological problems afflicting those on board.
Khalid said investigators have conducted 170 interviews and that more statements need to be collected.
Malaysian officials have said they believe someone intentionally diverted the plane, and that oit ultimately crashed into remote and treacherous waters off the northwest coast of Australia.
Ten aircraft and nine ships continued to search for any wreckage Wednesday, under favorable weather conditions.
Australian Prime Minister Tony Abbott said his country is committed to finding out what happened to the plane.
"It's one of the great mysteries of our time. It's a terrible tragedy," he said. "There are 239 devastated families. There are a lot of very concerned people right around the world, and Australia is leading the search and recovery effort - as is right, given that it all happened in our search-and-rescue zone. We owe it to the world. We owe it to those families to do whatever we reasonably can to get to the bottom of this."
The search is also expanding underwater, with the arrival of Britain's nuclear-powered submarine HMS Tireless.
Time is running out to detect the signal from the missing plane's flight data recorders, whose battery power usually lasts only 30 days.