Malaysian authorities concluded in their final report that they cannot determine the cause disappearance of Malaysia Airlines flight 370, which happened four years ago.

This has led to the resignation of Azharuddin Abdul Rahman, the head of Malaysia’s civil aviation authority.

The final report ruled out a suicidal pilot, hacked remotely, and the theory that “lithium-ion batteries and tropical fruit in its cargo hold” managed to “create a deadly cocktail that exploded mid-air.”

The report determined “that someone manually rerouted the plane after severing communications,” which led the investigators to believe that someone hijacked the plane. From The New York Post:

“We have examined the pilot, the flight officer. We are quite satisfied with their background, with their training, with their mental health, mental state. We are not of the opinion that it could have been an event committed by the pilot,” head investigator Kok Soo Chon told reporters in Kuala Lumpur, according to Australia’s The Age newspaper.

“But at the same time, we cannot deny the fact that there was an air turn-back,’’ which put the plane off course, he said. “We cannot deny the fact that, as we have analyzed, the systems were manually turned off with intent or otherwise.

“So we feel that there’s also one possibility that could account for all these,” the official said. “No matter what we do, we cannot exclude the possibility of a third person or third party or unlawful interference.”

Aviation experts went on TV in May and expressed their belief that the pilot deliberately caused the crash.

No one will know what happened to the flight since it disappeared in March 2014 as it carried 239 people from Kuala Lumpur to Beijing.

But the report showed major failures by the air traffic control center in Kuala Lumpur, which is why Rahman decided to resign. From CNN:

Azharuddin Abdul Rahman, the chairman of the Civil Aviation Authority of Malaysia (CAAM), said in a statement that while the report did not fault the Department of Civil Aviation, there was evidence Kuala Lumpur Air Traffic Control Center “did not comply with certain Standard Operating Procedures”.

“Over the past four years, I have tried my level best to assist in the search for MH370 and I am ever resolute in finding answers we all seek towards this unfortunate tragedy as we owe it to the families and loved ones,” he said. “I am saddened to have to leave under these circumstances.”

His resignation will take effect in 14 days.

The plane sent a message to Malaysian air traffic control at 1:20AM, but did not check in with the Vietnamese controllers when it flew into Vietnam airspace.

No one raised the alarm until 6:30AM. The report stated that controllers in Malaysia and Vietnam “should have sent sent up a red flag several hours earlier” while “[T]he radio controller in Kuala Lumpur also should have been monitoring its movement.”

Plus the plane’s four emergency local transmitters failed.