In one document, Aaron Alexis wrote: “An ultra low frequency attack is what I’ve been subject to for the last three months, and to be perfectly honest, that is what has driven me to this.”

Investigators are still trying to understand Alexis’s “pathway to violence,” Parlave told reporters. The etchings on his gun included “Not what y’all say!” and “Better off this way!”

Another scratched message, “My ELF weapon!,” and other evidence gathered from Alexis’s electronics indicate that the former Navy reservist thought he was being controlled by extremely low-frequency electromagnetic waves, according to the FBI. The Navy has legitimately used such technology, the FBI said, but these radio waves also have been at the center of conspiracies about government mind control.