The FBI released chilling video Wednesday that shows Navy Yard shooter Aaron Alexis moments before his deadly rampage. It has also unveiled a motive for the mass shooting, which left 12 people dead: The shooter's "delusional" belief that he was being manipulated by electromagnetic waves.
The video shows Alexis arriving by car and walking through the doors with a bag over his shoulder.
Later in the video, Alexis is visible in the hallway holding an armed, sawed-off shotgun. In part of the video, workers running from him are visible at the other end of the hallway.
The FBI, which released the clip on its YouTube account, said it has more graphic footage of the rampage that will not be released.
The video was just part of the information the FBI revealed at a press event today.
On the gun:
Investigators say Alexis bought a Remington 870 shotgun and a hacksaw to saw the barrel and stock off. Etched into the gun were the phrases "End to the torment!" "Not what yall say!" "Better off this way!" and "My ELF weapon!"
Investigators also say he got a handgun during the shooting and used that as well.
What is 'ELF'?
"There are multiple indicators that Alexis held a delusional belief that he was being controlled or influenced by extremely low frequency (ELF) electromagnetic waves," the FBI stated in a press release. "The etching of 'My ELF weapon!”' on the left side of the receiver of the Remington 870 shotgun is believed to reference these electromagnetic waves. In addition, a document retrieved from his electronic media stated, “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.”
The FBI also released a timeline of the shooter's actions that morning: