An official Malaysian investigation into the fate of Malaysia Airlines Flight 370, which disappeared four years ago and has not been found despite extensive searches, was unable to determine what happened to the plane, safety investigators said Monday.
The head of the safety investigation team, Kok Soo Chon, said the available pieces of evidence, including the plane’s deviation from its flight course and the switching off of a transponder, “irresistibly point” to unlawful interference.
But he added that the panel found no indication of who might have interfered or why, and that any criminal inquiry would be the responsibility of law enforcement authorities, not safety investigators.
An investigation into the pilot and first officer “could not detect any abnormality,” Mr. Kok said, and background checks on the passengers by local law enforcement agencies revealed “a clean bill of health for everybody.”
The disappearance of the flight is one of the enduring mysteries of aviation history, and has promoted all manner of conspiracy theories.
Mr. Kok said there had been no threats or credible claims of responsibility for the plane’s disappearance, which might have been expected as part of a plan to take it down intentionally.
The panel said it would disband after releasing the 495-page document, but it declined to call the report final.
“It is too presumptuous of us to say this is the final report,” said Mr. Kok, a former director-general of Malaysia’s Civil Aviation Department. “No wreckage has been found. The victims have not been found. How could this be final?”
Families of the 239 people who disappeared with the plane have been anticipating the report. While the document covered many theories into what happened to the Boeing 777, it gave no final determination.
“1,605 days of roller coaster, families still have no closure,” Voice370, a group of family members, said on its Facebook page after the report was released. “The team concluded that they were unable to determine the real cause for the disappearance of #mh370. Simply unacceptable as a ‘final’ report. How can we prevent another MH370 incident in future?”
Malaysia Airlines Flight 370 was heading north from Kuala Lumpur, Malaysia, to Beijing on March 8, 2014, when it deviated from its scheduled path, turning west across the Malay Peninsula. It is believed to have turned south after radar contact was lost and crashed somewhere in the southern Indian Ocean after running out of fuel.
After an air search of nearly two months, an underwater search was carried out, primarily by private contractors.
Investigators tried to determine where the plane went down by overlapping a 400-mile arc along which its final satellite communication was made with estimates of how much fuel it had left.
Ships scoured a zone of more than 46,000 square miles before calling off an official search last year that cost a total of $150 million.
The Malaysian safety investigators said Monday that they could not release their report until after the search had been concluded.
A small amount of debris from the plane has been found, including a part of the aircraft wing called a flaperon that was discovered on the French island of Réunion, east of Madagascar, in 2015.
An American lawyer found another piece, a gray triangle of fiberglass composite and aluminum with words “No Step” stenciled on one side, in Mozambique in February 2016.
The discovery of those objects support the theory that the plane broke apart upon entering the southern Indian Ocean, and that pieces that stayed afloat then traveled west on currents that run from Australia to Africa.
The investigators said Monday that they found several shortcomings in procedure among various bodies responsible for the safety of the flight.
The handover of responsibility for the flight from air traffic control in Malaysia to Ho Chi Minh City, Vietnam, was premature by three minutes, and the Vietnamese authorities were late in recognizing that the plane had vanished. But Mr. Kok said none of these factors were responsible for the plane’s disappearance itself.