Story highlights The official search for the plane was called off in January 2017

Ultimate fate of the 239 people on board remains unknown

(CNN) Three and a half years after Malaysian Airlines flight 370 disappeared, investigators say it is "inconceivable" that we are no closer to knowing its ultimate fate.

In January, the governments of Malaysia, Australia and China called off the search for the plane -- which disappeared en route from Kuala Lumpur to Beijing in March 2014 -- after more than 1,000 days of scouring a more than 710,000 square kilometer patch of the Indian Ocean.

"The reasons for the loss of MH370 cannot be established with certainty until the aircraft is found," the Australian Transport Safety Bureau (ATSB) said Tuesday in its final report on MH370.

"It is almost inconceivable and certainly societally unacceptable in the modern aviation era with 10 million passengers boarding commercial aircraft every day, for a large commercial aircraft to be missing and for the world not to know with certainty what became of the aircraft and those on board."

The new report exhaustively documents the efforts taken to find the plane, including a huge, years-long multi-country underwater search.