If the weapon is real, who is wielding it?

The U.S. has not officially blamed anyone yet—but all indicators point to Russia and its military intelligence unit, the GRU.

The recent National Academies of Sciences report noted there’s been “significant research in Russia/USSR” on pulsed radio frequency technology. The CIA has used mobile-phone data to locate Russian intelligence agents who worked on microwave-weapons programs in the same cities where CIA officers were afflicted, according to news reports. These weapons could be small enough to fit inside a van or even a backpack, and could target an individual up to 1,000 yards away, officials believe.

“It looks, smells, and feels like the GRU,” an official involved in the investigation told Politico.com.