Alexis moves through the hallways of Building #197 carrying the Remington 870 shotgun. Courtesy FBI.

The FBI released chilling surveillance video and images today showing Navy Yard shooter Aaron Alexis entering the Naval Sea Systems Command headquarters last week and moving through Building 197 with a shotgun.

Valerie Parlave, assistant director of the FBI’s Washington field officer, said at a press conference today that the agency now has a “greater understanding of recent movements and activities” by Alexis, who they say acted alone.

Parlave said Alexis used a shotgun, which had been altered with a sawed off barrel and stock, and a pistol he obtained during the shooting to kill 12 people last Monday. Etched on the shotgun were the phrases “End to the torment,” “Not what y’all say,” “Better off this way” and “My ELF weapon.”

There’s no indication that Alexis was targeting specific individuals, Parlave said, and it’s apparent he was prepared to die. Parlave said there are “multiple indicators” that Alexis held a delusional belief that he was being controlled by extremely low frequency 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.”

Here’s a timeline of the shooting, provided by the FBI.

7:53 a.m. – Alexis’ rental car, a blue Toyota Prius with New York plates, entered Parking Garage #28 at the Washington Navy Yard, located directly across from Building #197.
8:08 a.m. – Alexis exited Parking Garage #28 on foot carrying a backpack. Alexis entered Building #197 and proceeded to the elevator.
8:09 a.m. – Alexis exited the elevator on the fourth floor and entered the men’s bathroom carrying a backpack and a clipboard.
8:15 a.m. – Alexis crossed the hallway into the 4 West area of Building #197 with shotgun, but without the backpack or a clipboard.
8:16 a.m. – Alexis shot the first victim in the 4 West area of Building #197.
8:17 a.m. – First 911 call is received from the fourth floor of Building #197.
8:20 a.m. – Alexis left the fourth floor using the stairs and entered the third floor.
8:28 a.m. – Alexis appeared on the first floor.
8:57 a.m. – Alexis returned to the third floor.
9:25 a.m. – Law enforcement shoot and kill Alexis on the third floor.

Alexis moves through the hallways of Building #197 carrying the Remington 870 shotgun. Courtesy FBI.