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Malaysia police say Flight 370 probe may take a long time and may end without a conclusion

  • Chief Executive and Director General of the International Air Transport Association (IATA) Tony Tyler speaks during the IATA Ops Conference in Kuala Lumpur, Malaysia, Tuesday, April 1, 2014. The IATA said the disappearance of a Malaysia Airlines plane highlights the need for security improvements both in tracking aircraft and screening passengers before they board planes. The 3-week hunt for Flight 370 has turned up no confirmed sign of the Boeing 777, which disappeared March 8 with 239 people on board bound for Beijing from Kuala Lumpur. (AP Photo/Lai Seng Sin)

    Chief Executive and Director General of the International Air Transport Association (IATA) Tony Tyler speaks during the IATA Ops Conference in Kuala Lumpur, Malaysia, Tuesday, April 1, 2014. The IATA said the disappearance of a Malaysia Airlines plane highlights the need for security improvements both in tracking aircraft and screening passengers before they board planes. The 3-week hunt for Flight 370 has turned up no confirmed sign of the Boeing 777, which disappeared March 8 with 239 people on board bound for Beijing from Kuala Lumpur. (AP Photo/Lai Seng Sin)  (The Associated Press)

  • Chief Executive and Director General of the International Air Transport Association (IATA) Tony Tyler, left, talks to Malaysia's Department of Civil Aviation Director General Azharuddin Abdul Rahman after Azharuddin stopped his speech halfway and requested journalists to leave the conference room during the IATA Ops Conference in Kuala Lumpur, Malaysia, Tuesday, April 1, 2014. (AP Photo/Lai Seng Sin)

    Chief Executive and Director General of the International Air Transport Association (IATA) Tony Tyler, left, talks to Malaysia's Department of Civil Aviation Director General Azharuddin Abdul Rahman after Azharuddin stopped his speech halfway and requested journalists to leave the conference room during the IATA Ops Conference in Kuala Lumpur, Malaysia, Tuesday, April 1, 2014. (AP Photo/Lai Seng Sin)  (The Associated Press)

  • A woman, one of the relatives of Chinese passengers aboard the missing Malaysia Airlines flight MH370, looks at messages of wish for the passengers, at a hotel in Beijing, China Tuesday, April 1, 2014. Although it has been slow, difficult and frustrating so far, the search for the missing Malaysia Airlines jet is nowhere near the point of being scaled back, Australia's Prime Minister Tony Abbott said. The three-week hunt for Flight 370 has turned up no sign of the Boeing 777, which vanished March 8 with 239 people bound for Beijing from Kuala Lumpur. (AP Photo/Andy Wong)

    A woman, one of the relatives of Chinese passengers aboard the missing Malaysia Airlines flight MH370, looks at messages of wish for the passengers, at a hotel in Beijing, China Tuesday, April 1, 2014. Although it has been slow, difficult and frustrating so far, the search for the missing Malaysia Airlines jet is nowhere near the point of being scaled back, Australia's Prime Minister Tony Abbott said. The three-week hunt for Flight 370 has turned up no sign of the Boeing 777, which vanished March 8 with 239 people bound for Beijing from Kuala Lumpur. (AP Photo/Andy Wong)  (The Associated Press)

Malaysia's national police chief has warned that the investigation into what happened to Malaysia Airlines Flight 370 may take a long time and may never determine the cause of the tragedy.

Khalid Abu Bakar said Wednesday that the criminal investigation is still focused on four areas — hijacking, sabotage and personal or psychological problems of those on board the plane.

"Investigations may go on and on and on. We have to clear every little thing," Khalid 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."

The plane disappeared March 8 on a flight to Beijing from Kuala Lumpur with 239 on board. No trace of the plane has been found.