“Possibility” is one word, but it’s starting to look like “probability” is a better one. Ukrainian investigators in Iran suspect that the plane that exploded and crashed near Tehran during the missile attack on American bases in Iraq got shot down, the Washington Post reports this morning. Nothing else appears to fit the initial set of facts, and certainly not Iran’s initial explanation of the incident:

Ukrainian investigators are considering the possibility that an antiaircraft missile might have hit a passenger jet that crashed near Tehran, killing all 176 aboard, as an initial report released Thursday by Iran said the plane was on fire while still in the air.

The preliminary Iranian investigation cited witnesses saying the plane was burning and was turning back to Tehran because of the “problem” when it went down Wednesday. …

The Ukraine International Airlines flight — bound for the Ukrainian capital, Kyiv — departed Tehran at 6:12 a.m. on Wednesday and was approaching 8,000 feet when it abruptly lost contact with ground control, officials said.

The report from Iran’s Civil Aviation Organization said eyewitnesses on the ground and among the crew of another flight in the vicinity reported seeing a fire while the Boeing 737 jet was still in the air, followed by an explosion when it crashed near an amusement park.

“The trajectory of the collision indicated that the plane was initially moving toward the west, but after encountering a problem, it turned to the right and was approaching the airport again at the time of the crash,” Ali Abedzadeh, head of the Civil Aviation Organization, said in the report.

Initially, the Ukrainians accepted the Iranian explanation and tweeted out that terrorism didn’t play a role in the crash. It didn’t take long for them to delete that statement, however, perhaps especially after viewing the video purportedly of the plane engulfed in flames while still in the air. An NTSB official told CNN this morning that the video gives him “shivers,” because no normal failure would have caused this kind of fireball in the air, not without some warning from the pilot:

Officially, the Ukrainians are keeping open the possibilities of pilot error or mechanical malfunction. That’s only pro forma, however. The plane itself was less than four years old and didn’t have any issues before this flight, and what kind of pilot error would turn a healthy plane into a fireball at 8,000 feet with no notice whatsoever? Unofficially, Ukraine discounts that possibility entirely, saying that the flight crew was too experienced to have committed such an error, and also to have not reported a problem promptly. The catastrophe had to occur suddenly and totally, making it impossible for the pilots to communicate the emergency, and that doesn’t sound likely to have been either pilot error or mechanical failure.

So what did happen? Rumors of Russian anti-aircraft missile wreckage at the site have not yet been confirmed, but it would provide the most complete answer to this mystery. Ukraine has unfortunate experience with this kind of incident, having had Russian-backed rebel forces shoot down a Malaysian Air flight in July 2014 thinking it was a military sortie. The timing of the explosion, coming so soon after the Iranian missile attacks on US forces in Iraq, lends itself to that explanation, too.

Could an Iranian anti-aircraft unit have gotten spooked by the flight and misinterpreted it as an American counterattack? That has an unfortunate history in this region, too. Thirty-two years ago, the USS Vincennes shot down an Iranian Air commercial flight after mistaking it for an F-14, killing all 290 people on board. The commander of the Vincennes had gone into Iranian waters and gotten engaged in a firefight with some gunboats, and the command misinterpreted the flight data as a supporting Iranian attack on the ship. The Airbus at the time was ascending on a normal flight path for passenger service, however, and the Vincennes crew didn’t follow proper protocol in assessing the threat. The US wound up paying over $60 million in compensation to the families of the deceased, although we never admitted culpability for it.

At least at first blush, it appears that the Iranians made the same mistake. There was no other good reason for shooting down an airliner, especially in that location, where the Americans can’t really get blamed for it. We conducted no raids that night, and no other anti-aircraft units found any reason to fire their weapons, apparently. The possibility apparently worries the Iranians enough that they are refusing to release the black boxes, although that would be from a lack of information on them. The pilot almost certainly wouldn’t have seen a missile in time to react or to identify it before the explosion, and the sudden end of data on the black boxes would point to no other explanation — or source.