A March report from the National Academy of Sciences found that "directed, pulsed radio frequency energy" was the most likely cause of the strange set of symptoms. While the report was carefully written not to overstate its findings, it offered some of the clearest public evidence to date that the incidents could be attacks, attributing the afflictions to "pulsed" or "directed" energy.
Some personnel have been seriously injured from the alleged attacks, with at least one career CIA officer forced to retire last year and diagnosed with a traumatic brain injury.
This story has been updated with comments from the White House and also the Director of National Intelligence.