WASHINGTON (AP) -- The Washington Navy Yard gunman did not target specific individuals when he opened fire inside a building, killing 12 people, and was under a delusional belief that he was being controlled by extremely low frequency electromagnetic waves, the FBI said Tuesday.
Records recovered from Aaron Alexis's computer and cellphone reveal paranoia and mental health problems that authorities are investigating as the root cause.
"Ultra-low frequency attack is what I've been subject to for the last 3 months, and to be perfectly honest that is what has driven me to this," read a document agents recovered from Alexis after the shooting. He had also written "my ELF weapon" - an apparent reference to extremely low frequency waves - on a shotgun he used in the rampage.
Alexis, a 34-year-old former Navy reservist and IT contractor, used a valid badge to access the Navy Yard on the morning of Sept. 16 with a sawed-off Remington shotgun he had purchased two days earlier. He was killed by a U.S. Park Police officer following a rampage and shootout that police now say lasted for about an hour.
Authorities say Alexis had only recently started his job, and that although there was a "routine performance-related issue addressed to him" on the Friday before the shooting, there's no indication that he targeted particular co-workers or was motivated by problems in the workplace, said Valerie Parlave, head of the FBI's Washington field office.
"There is no indication that this caused any sort of reaction from him. We have not determined there to be any previous relationship between Alexis and any of the victims," Parlave said.
At the Pentagon on Wednesday, Deputy Secretary Ash Carter said the department will complete three separate reviews in late December, including internal and independent assessments of base safety procedures as well as the security clearance process.
"Bottom line is, we need to know how an employee was able to bring a weapon and ammunition onto a DoD installation, and how warning flags were either missed, ignored or not addressed in a timely manner," Carter said during a Pentagon briefing.
Carter said the reviews will include consideration of Navy Secretary Ray Mabus' recommendation that the department require that all police reports, not just arrests or convictions, involving an individual be included in background checks.
The Defense Department's internal review will be coordinated by the Pentagon's top intelligence official, Under Secretary Michael Vickers, and the independent review will be spearheaded by retired Navy Adm. Eric Olson and Paul Stockton, the former assistant secretary for homeland defense. A Navy review will be finished by the end of October; initial findings of the two larger reviews are due to the defense secretary by Nov. 15; and the final overall report will be done by Dec. 20.