Until today the White House hadn’t said much about culpability, only that it was on Castro’s government to find out where the “sonic attacks” are coming from and to stop them. But now John Kelly has pointed a finger:

White House chief of staff John Kelly says the United States believes that Cuban President Raul Castro’s government could stop attacks on U.S. diplomats.

Kelly isn’t elaborating on why the U.S. believes Cuba could stop it. Previously, the United States has said merely that it was Cuba’s responsibility under international law to protect diplomats serving on its soil.

So the U.S. has reason to believe that Castro knows who’s behind this, assuming he’s not the culprit himself. That deepens an already deep mystery: Why would Cuba have started attacking American diplomats in the first place? Before you say “they hate Trump,” who’s criticized Castro, remember that the sonic attacks began last December when Obama was still in the White House and doing everything he could do to make Cuban-American relations warm and fuzzy before he left. It would have been inexplicable for Castro to jeopardize that by targeting Americans in Havana, especially not knowing how the belligerent and unpredictable new president would react.

In a year full of bizarre news on every front the sonic attack saga is quietly one of the strangest. American officials have been studying it for months, using the best technology the U.S. has to try to get to the bottom of it, and … nothing. They still have no idea what’s going on. (Or so they say.) But they do, at least, have proof that there *is* a sound that the Americans have been hearing. The AP has a recording of it, which you can listen to below. It would drive me to distraction if I had to listen to it for more than a minute but the effect on U.S. diplomats went way beyond irritation. Some reportedly have suffered “mild traumatic brain injury” from being exposed to it. Others have suffered hearing loss. What kind of weapon can do that? Officially, the U.S. has no idea:

It sounds sort of like a mass of crickets. But not quite. A high-pitched whine, but from what? It seems to undulate, even writhe. Listen closely: Some hear multiple, distinct tones colliding in a nails-on-the-chalkboard effect…

A closer examination of one recording reveals it’s not just a single sound. Roughly 20 or more different frequencies, or pitches, are embedded in it, the AP discovered using a spectrum analyzer, which measures a signal’s frequency and amplitude…

“What it is telling us is the sound is located between about 7,000 kHz and 8,000 kHz. There are about 20 peaks, and they seem to be equally spaced. All these peaks correspond to a different frequency,” said Kausik Sarkar, an acoustics expert and engineering professor at The George Washington University who reviewed the recording with the AP.

One possibility previously considered by experts was microwaves — that the Cubans were literally frying Americans from a distance, which could conceivably produce a ringing sound in the target’s ears. It wouldn’t produce audio that could be captured on a recording device, though, in which case how to explain what you hear below? A more plausible theory is that the AP recording only captures part of what the diplomats are experiencing; what’s making them sick is an additional tone, either infrasonic or ultrasonic, that can’t be heard by human ears but can be felt by human organs. That concept is behind the legend of the “brown note,” an infrasonic frequency that will supposedly make humans fill their drawers with, er, “brownness” when they’re exposed to it. But no one’s been able to actually produce the “brown note.” Ultrasonic frequencies can produce nausea and discomfort in targets but the Times noted a few days ago that they don’t travel very far and would be mostly deflected by the walls of the embassy.

So baffled are experts about what this might be that they’ve turned to mass hysteria as a possible explanation. Can mass hysteria cause, er, mild traumatic brain injury and central nervous damage? Sort of. “We are talking about genuine symptoms that people have of dizziness, of headaches, of hearing problems, which they are not faking,” said one neurologist to the Guardian. A few people in a small, stressful community experience odd “symptoms,” others suspect they’re being targeted, and suddenly you have an “outbreak” or a mass “attack.” Just one problem, though: Again, how do you explain this recording? Is it some ingenious psy op by the Cubans aimed at triggering mass hysteria, possibly introduced when a few Americans were under the weather for wholly unrelated reasons in the belief that the suspicious mystery noise would eventually be suspected as the cause?

Maybe it is a microwave weapon of some type and the noise that’s being produced comes from the device itself, not the wave that’s doing the damage. But if there’s a device around that’s powerful enough to damage people’s brains from a distance, someone should have spotted it or at least have a sense of what it is. Instead, nothing.