The real cause behind the mysterious disappearance of Flight MH370 may never be known, Malaysian police warned on Wednesday as the frustrating search for the crashed airliner continued in the Indian Ocean without any headway.

“Criminal investigations may go on and on and on. We have to clear every little thing,” Inspector-General of Police Khalid Abu Bakar said.

“At the end of the investigations, we may not even know the real cause. We may not even know the reason for this incident,” he told reporters in Kuala Lumpur.

After intense investigations, some clues into the missing MH370 have been derived after interrogating 170 people, including family members of passengers, pilot and co-pilot, Mr. Khalid said, adding that more people will be quizzed.

Malaysian Prime Minister Najib Razak is in Australia on a two-day tour to oversee the search for the plane.

On the 25th day of the multinational search operations, a British nuclear submarine joined the hunt, about 1,500 km northwest of Perth.

Up to 10 planes and nine ships participated in Wednesday’s search.

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