Alexis moves through the hallways of Building #197 carrying the Remington 870 shotgun.
WASHINGTON -- The FBI says there is no indication that the Navy Yard shooter targeted any specific individuals when he opened fire inside a building, killing 12 people.
PHOTOS | FBI photos of gunman Aaron Alexis going through the Navy Yard
VIDEO | FBI releases video of Navy Yard gunman going through building
Valerie Parlave, head of the FBI's field office in Washington, said Wednesday during a news conference that investigators are continuing to explore the background and motivations of 34-year-old Aaron Alexis. However, she says Alexis had a well-documented history of mental health issues.
Parlave says Alexis held a delusional belief that he was being controlled by extremely low frequency waves, or ELF waves. Alexis had written "my ELF weapon" on a shotgun he used in the rampage.
Alexis, a former Navy reservist and IT contractor, was killed in a shootout with police.
MORE COVERAGE OF NAVY YARD SHOOTING:
- Remembering the victims of the attack
- Aaron Alexis arrested in DeKalb County in 2008
- 12 Killed in the Navy Yard shooting - A look at what happened
- Photos from the day of the Navy Yard Shooting