Navy Yard shooting video footage released by FBI shows the horrific attack by Aaron Alexis on the Washington Navy Yard that killed 12 people.<br /><br />According to the FBI, the video footage from closed-circuit video cameras shows Aaron Alexis at the Washington Navy Yard on September 16, 2013. <br /><br />Alexis is first seen driving his rental car, a blue Toyota Prius, through the Washington Navy Yard main gate.<br /><br />Alexis next can be seen entering Building #197 carrying a backpack. Alexis had legitimate access to the Washington Navy Yard as a result of his work as a contractor and he utilized a valid pass to gain entry to the building.<br /><br />Alexis moves through the hallways and a stairwell of Building #197 carrying a Remington 870 shotgun.<br /><br />Alexis acted alone, the FBI concluded after an investigation. <br /><br />The FBI released the following timeline detailing Alexis' activity that day:<br /><br />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.<br /><br />8:08 a.m. -- Alexis exited Parking Garage #28 on foot carrying a backpack. Alexis entered Building #197 and proceeded to the elevator.<br /><br />8:09 a.m. -- Alexis exited the elevator on the fourth floor and entered the men's bathroom carrying a backpack and a clipboard.<br /><br />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.<br /><br />8:16 a.m. -- Alexis shot the first victim in the 4 West area of Building #197.<br /><br />8:17 a.m. -- First 911 call is received from the fourth floor of Building #197.<br /><br />8:20 a.m. -- Alexis left the fourth floor using the stairs and entered the third floor.<br /><br />8:28 a.m. -- Alexis appeared on the first floor.<br /><br />8:57 a.m. -- Alexis returned to the third floor.<br /><br />9:25 a.m. -- Law enforcement shoot and kill Alexis on the third floor.