Wednesday afternoon, the FBI released a video of Aaron Alexis as he prowled through the Washington Navy Yard, armed with a shotgun. The FBI also released a timeline of the events leading up to the shooting.

From the FBI’s press release:

On Saturday, September 14, 2013, Alexis purchased a Remington 870 shotgun and ammunition at a gun shop in Northern Virginia. On the same day, Alexis also purchased a hacksaw, among other items, at a home improvement store in Northern Virginia.

On the morning of Monday, September 16, 2013, Alexis arrived at the Washington Navy Yard. Alexis had legitimate access to the Navy Yard as a result of his work as a contractor and he utilized a valid pass to gain entry to Building #197. Shortly after his arrival in the building and over the course of approximately one hour, Alexis used the Remington 870 shotgun and a Beretta handgun he obtained during the course of his shooting to kill 12 victims and wound four surviving victims before he was shot and killed by law enforcement officers. Investigation to date has determined that Alexis acted alone.

The following timeline details Alexis’ activity during the morning of September 16, 2013:

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.

And here are three photos of the shotgun used by Alexis.

The FBI also published a slideshow of pictures of Alexis in the Navy Yard.