WASHINGTON -- Aaron Alexis, the shooter who police say killed 12 people at the Navy Yard here last week, believed that his mind was being controlled by "extremely low frequency" electromagnetic waves, the senior law enforcement official overseeing the investigation said Wednesday.
In a document retrieved by investigators from one of his electronic devices, Alexis, a former Navy reservist and military contractor, said "ultralow frequency attack is what I've been subject to for the last three months," said the senior official, Valerie Parlave, assistant director in charge of the FBI's Washington Field Office. "To be perfectly honest, this is what has driven me to this," Alexis wrote, according to Ms. Parlave.
The phrases "my ELF weapon," "end to the torment," "not what ya'll say" and "better off this way," were etched into the side of the shotgun that Alexis used to kill many of the victims, she said.
Ms. Parlave, who spoke at a news conference outside the FBI's Washington Field Office, said ELF was a technology the Navy used for submarine communication. But some conspiracy theorists believe, she said, that it is the "weaponization of remote neuro-frequencies for government monitoring and manipulation of unsuspecting citizens."
In communications obtained by the authorities, Alexis said "he was prepared to die in the attack and accepted death as the inevitable consequence of his actions," Ms. Parlave said. She also said investigators believed that Alexis had targeted his victims randomly and was not seeking to shoot his co-workers.
The FBI on Wednesday also released surveillance video that shows Alexis, who was killed in a shootout with police at the Navy Yard, arriving alone in a car at the facility's parking garage. He can be seen setting up his rifle and walking down a hallway, ducking in and out of doorways, before opening fire.
The video, which appears to be edited to exclude images of people being shot, does not show him in the atrium area overlooking the cafeteria where several people were killed as they were getting breakfast. Alexis is seen with the shotgun that FBI officials said was used in the shootings.
Also Wednesday, a senior defense official said the Pentagon had started three separate reviews of its security procedures in response to the shooting. Deputy Defense Secretary Ashton B. Carter told reporters that the Office of the Secretary of Defense, the Navy and an independent panel were looking into potential flaws in base security, background investigations and other areas that could have allowed the Navy Yard shooting to occur.
"The 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," he said.
Mr. Carter confirmed that the Department of Defense was considering including more information from law enforcement in future background checks for personnel. Navy Secretary Ray Mabus recently recommended that such checks look at all available police reports, regardless of whether they resulted in charges being filed or convictions.
Alexis had two gun-related incidents in his past, and was jailed briefly in Georgia, but those incidents did not raise red flags during background checks.
"We have to confirm the truth of these things," Mr. Carter said. "But I think that what certainly caught my eye -- and the secretary's eye -- is exactly that kind of thing: evidence that there was behavior well before the Washington Navy Yard incident, which, had it been spotted and understood to be indicative of this possibility, might have led to an intervention that would have prevented this."
Mr. Carter said the reviews would also look at the contractors tasked with checking personnel. But he said the question of whether the responsibility for conducting security investigations should be returned to the government would be considered by the administration's governmentwide investigation. USIS, the company that conducted background checks of both Alexis and Edward J. Snowden, the former government contractor who leaked national security secrets, is under investigation by the Office of Personnel Management.
A report incorporating findings of all three reviews is to be delivered to Defense Secretary Chuck Hagel by Dec. 20.
Hewlett-Packard on Wednesday terminated its working relationship with the computer services firm that employed Alexis for about a year, The Experts Inc. Alexis worked at numerous military installations for The Experts, including the Navy Yard.
Hewlett-Packard "has lost all confidence in The Experts' ability to meet its contractual obligations and serve as an HP subcontractor," said Henry Dreschler, Hewlett-Packard's director of global contingent labor, in a letter to The Experts' chief executive, Thomas E. Hoshko. The letter, a copy of which The New York Times obtained, added, "It is clear The Experts failed to meet HP's expectations of its subcontractors and suppliers."
Mr. Hoshko did not returns calls for comment.