The FBI has released a video of Aaron Alexis walking around the Washington D.C. Navy Yard building and pointing his shotgun into several offices on Sept. 16.
The short YouTube video (below) from closed-circuit video cameras shows Alexis driving his black rental car into the Navy Yard's main gate.
Alexis then enters Building #197 carrying a backpack with his guns inside. The alleged shooter had access to the Navy Yard because he was a government contractor.
The video then cuts to Alexis sneaking through hallways and a stairwell while carrying his Remington 870 shotgun (he also had a Beretta 9mm semiautomatic pistol).
Alexis was later killed by Washington D.C. police.