The FBI has released chilling video of the gunman from the shooting at the Washington Navy Yard.
Surveillance camera footage shows Aaron Alexis pulling his rental car into a garage, entering the building with a bag, and then moving through a corridor with a sawed-off shotgun.
The video captures Alexis stalking the halls, ducking and crouching around a corner, and walking briskly down a flight of stairs.
The FBI said there is no indication Alexis targeted any specific individuals when he opened fire inside the building, killing 12 people.
Officials said he left a note saying he was driven to kill by months of bombardment with extremely low-frequency radio waves and that he was hearing voices.
"It appears that Mr. Alexis, in a scenario that we've seen far too often, quite frankly, was a mentally unstable individual," U.S. Attorney for the District of Columbia Ronald Machen said.
Meanwhile, the Pentagon plans to review safety procedures and the security clearance process at the Navy Yard.
safety procedures and the security clearance process at the navy yard.