With no wreckage found yet that can be linked to Flight MH370 and time beginning to run out for a homing beacon on the 'black box' flight data recorder, Malaysia's police chief says the mystery of the missing airliner may never be solved.
Khalid Abu Bakar says the criminal investigation into the disappearance of the Malaysia Airlines flight could "go on and on and on.
"We have to clear every little thing," he told reporters. "At the end of the investigations, we may not even know the real cause. We may not even know the reason for this incident."
His remarks follow a similar assessment on Tuesday from the head of the Australian-led search effort, retired Air Chief Marshal Angus Houston.
In comments on Wednesday, Bakar said the investigation is now focused on pilot Zaharie Ahmad Shah and co-pilot Fariq Abdul Hamid, and the cabin crew after police had "cleared" all passengers on the plane's manifest.
Meanwhile, the British submarine HMS Tireless has arrived in the southern Indian Ocean to join in the search of some 85,000 square miles far off the west coast of Australia, but fog and thunderstorms in the area were complicating efforts to find the Boeing 777 that disappeared seemingly without a trace on March 8.
Australia's Joint Agency Coordination Centre, or JACC, issued a statement on Wednesday saying "up to 10 planes and nine ships" were engaged in the search.
"The weather forecast for today's search is for marginal conditions, with areas of broken cloud, sea fog and isolated thunderstorms, reducing visibility," the statement said.
On Tuesday, Malaysia authorities released a full transcript of communications between the flight and the control tower in Kuala Lumpur.