Malaysia's police chief says the reason for the disappearance of Malaysia Airlines flight MH370 on 8 March may never be known.
Khalid Abu Bakar: "We have to clear every little thing." Photo: AFP
Khalid Abu Bakar says the criminal investigation could "go on and on and on. We have to clear every little thing."
"At the end of the investigations, we may not even know the real cause. We may not even know the reason for this incident."
Mr Khalid says police have cleared all the passengers with regard to the four key areas being investigated: hijacking, sabotage, and psychological and personal problems.
He adds that more than 170 interviews had been done with family members of the pilots and crew members, and that even cargo and food served on the plane are being investigated in case of sabotage.
Ten planes and nine ships are searching the southern Indian Ocean for traces of the plane, and a British submarine has also joined the hunt.
The head of Australia's Joint Agency Coordination Centre, Angus Houston, says it's the most challenging operation he has ever seen, and warns that search efforts "could drag on for a long time".
"The last known position [of the plane] was a long, long way from where the aircraft appears to have gone," complicating the task, he says.
Several floating objects have been found in recent days, but none is believed to belong to the missing plane.
Meanwhile, Malaysian leader Najib Razak is in Perth to visit the search centre headquarters and thank all those involved.
Australian Prime Minister Tony Abbott said on Thursday his country is doing everything possible to find the missing plane.
At a joint news conference, Mr Abbott said it is probably one of the most complex searches ever undertaken, but every day more information is turning up.
The Australian Maritime Safety Authority said on Thursday search area is shifting a little to the north.
