CANBERRA, Australia—Investigators believe debris found off Tanzania in June offers the best new clue to the final moments of Malaysia Airlines Flight 370, including whether it was under pilot control.

The Australian Transport Safety Bureau, which has spent weeks studying the piece—a main flap from a Boeing 777, which experts say is “highly likely” to be from Flight 370—aims to complete its analysis in around two weeks. Its conclusions will be part of a broader report to be reviewed by experts, including from Boeing Co., before being released to the public.

Investigators continue to seek answers to one of the world’s biggest aviation mysteries even as governments prepare to suspend the search after months spent scouring the floor of the southern Indian Ocean failed to find any trace of the plane. Flight 370 vanished from radar en route to Beijing from Kuala Lumpur on March 8, 2014, with 239 people on board.

Authorities have long believed the plane wasn’t under human control at the time of its apparent crash, based on communications between the aircraft and an Inmarsat PLC satellite. That communications data—central to fixing on a 120,000 square-kilometer search area, more than 90% of which has now been covered—suggest Flight 370 was plummeting at a rate of at least 12,000 feet a minute when it entered the water.

However, another theory—that the plane was in a controlled glide following a loss of engine power—hasn’t been ruled out, though authorities consider it less likely. While either theory would lead to largely the same search area, the edges would vary; a simulation shows the aircraft, starting from 40,000 feet, could have gone an extra 140 miles if under control.