Remember this? In mid-March, a Boeing 737 owned and operated by China Eastern airlines appeared to simply drop out of the sky, almost completely vertical, while showing no other obvious signs of failure. The crash instantly killed everyone on board.

This, by the way, wasn’t the same model of 737 that caused other crashes. So what went wrong? One analyst said a couple of says later that the evidence pointed to the flight crew rather than the plane itself, perhaps especially because the dive got briefly interrupted and reversed before plunging once again:

American officials working with China’s investigators have reviewed the flight data, and that points to one conclusion:

Flight data indicates someone in the cockpit intentionally crashed a China Eastern jet earlier this year, according to people familiar with U.S. officials’ preliminary assessment of what led to the accident.

The Boeing 737-800 was cruising at high altitude when it suddenly pitched into a near-vertical descent, plummeting into a mountain at extreme speed. Data from a black box recovered in the crash suggests inputs to the controls pushed the plane into the fatal dive, these people said.

“The plane did what it was told to do by someone in the cockpit,” said a person who is familiar with American officials’ preliminary assessment, which includes an analysis of information extracted from the plane’s damaged flight-data recorder.

Hoo boy. There is more indirect evidence that investigators are pursuing that as an explanation too, as the Wall Street Journal notes. Boeing has not issued any new guidance on safety issues for the 737-800 as a result of this crash, for one thing, and neither has the FAA or other air agencies. China’s investigators likewise have not identified any mechanical issues with this plane, let alone any that would create an uncontrollable vertical dive.

If the flight data recorder showed the controls being used to create the dive, that raises a number of questions. First, did one of the pilots choose to crash the plane? Presumably they would have the only access to the controls. Someone else could have broken into the cockpit, a scenario unfortunately all too familiar to Americans, but China Eastern says that pilots never sent any emergency signals that presumably would have been triggered by an assault on the cockpit. Of course, one might have expected the other pilot to have attempted such a signal if his partner had suddenly decided to commit suicide. If it was only one pilot, that would explain the reported interruption in the dive, but not why the other pilot didn’t signal an emergency.

What if it were both pilots? If so, that makes the purported interruption of the dive inexplicable. That makes it much more likely that there was a fight in the cockpit, but at least it would explain why no emergency call was made. The cockpit voice recorder, which was recovered from the site as well, might provide more insight into the motives of the pilot(s), but apparently that information has not yet been made available.

That could answer the most pressing question if the crash was deliberate: why would either or both pilots crash the plane, especially without warning? It could have been a mental-health episode, or some kind of protest. China’s government has become much more oppressive in recent years, plus there’s also that genocide against Muslim Uighurs taking place in Xinjiang. If any of those were the motive, though, one would think that the plane would have been used as a guided missile, a la 9/11, aimed at a government facility or perhaps the military command around the concentration camps. Why waste that potential with a vertical dive into an unpopulated area, especially with pilots capable of doing whatever they wished with their plane? There isn’t a scenario that fits all of the components of this event.

Except the mental illness explanation, of course, where rationality becomes optional. ABC News reports that investigators have found “issues” with one of the pilots:

Investigators also looked into one of the pilots’ personal lives and background and believe he may have been struggling through certain issues right before the crash, ABC News has learned.

“Certain issues” covers a lot of ground, of course. And even if they establish that this was a pilot with a psychotic break of some sort, it still leaves the question of why the other pilot couldn’t or didn’t seize control of the airplane. The voice recorder, which was recovered first, may give investigators more insight into that. Maybe.

We may know the how of the China Eastern crash now. We may never grasp the why.