The report, obtained by BuzzFeed News via a Freedom of Information Act request, was originally classified as “secret.” It concluded that the sounds accompanying at least eight of the original 21 Havana syndrome incidents were “most likely” caused by insects. That same scientific review also judged it “highly unlikely” that microwaves or ultrasound beams — now widely proposed by US government officials to explain the injuries — were involved in the incidents. And though the report didn’t definitively conclude what caused the injuries themselves, it found that “psychogenic” mass psychology effects may have played a role.

“No plausible single source of energy (neither radio/microwaves nor sonic) can produce both the recorded audio/video signals and the reported medical effects,” the JASON report concluded. “We believe the recorded sounds are mechanical or biological in origin, rather than electronic. The most likely source is the Indies short-tailed cricket.”

The report’s findings fly in the face of a medical report commissioned by the State Department and published by a National Academies of Sciences panel last year, which found that microwaves were the “most plausible” cause of the symptoms. That panel was not provided with the JASON report as part of its assessment, the NAS told BuzzFeed News.