WASHINGTON - The Federal Bureau of Investigation released a surveillance video and photos of Navy Yard shooter Aaron Alexis on Wednesday, and said he believed electromagnetic waves had been controlling him for months before the rampage that killed 12 people.
"We have found relevant communications on his electronic media, which referenced the delusional belief that he was being controlled or influenced by extremely-low-frequency electromagnetic waves for the past three months," said Ms Valerie Parlave, the FBI assistant director in charge of the Washington field office.
The surveillance video released by the FBI showed Alexis, 34, driving a rented blue Toyota Prius into a Navy Yard carpark shortly before 8am on Sept 16. He then entered the Naval Sea Systems Command building, the site of the shootings, through a door.
The brief video also shows Alexis, armed with a Remington shotgun, descending a stairway and walking along corridors in a crouched position, weapon at the ready.
Ms Parlave said Alexis, a government technology contractor, had the shotgun, which had a sawn-off barrel and stock, and a pistol he obtained during the shooting.
Scratched onto the shotgun were the phrases "End to the torment", "Not what y'all say", "Better off this way" and "My ELF weapon", photos released by the FBI showed. "ELF" is believed to stand for "extremely low frequency".
Alexis shot his first victim at 8.16am.
He was killed by police on the third floor after exchanging fire with them for an hour.