WASHINGTON (AP) — In the final months of his life, Aaron Alexis complained of hearing voices talking to him through a wall and of microwave vibrations that he said entered his body and prevented him from sleeping. His delusional belief that he was being bombarded by extremely low-frequency radio waves escalated to the point that, before embarking on a murderous rampage that killed 12 people at the Washington Navy Yard, he left behind this note:

“Ultra-low frequency attack is what I’ve been subject to for the last 3 months, and to be perfectly honest that is what has driven me to this,” read an electronic document FBI agents recovered after the shooting.