The officials cautioned they do not yet know what, if anything, Alexis meant in the etchings.
ELF generally stands for “extremely low frequency” and can refer to weather or communications efforts, among other things.
Alexis, who was battling mental health issues, told police in Rhode Island in August that he was hearing voices of three people who had been sent to follow him and keep him awake and were using “some sort of microwave machine” to send vibrations into his body, preventing him from falling asleep, according to police reports.
The law enforcement officials said they do not know whether he was referring to those vibrations in his carvings. The Navy has used extremely low frequencies in several capacities, including a joint effort with the Air Force on the High Frequency Active Auroral Research Program (HAARP). HAARP is often cited by conspiracy theorists.
The new details came as federal officials continued to wrestle with shortcomings in the military background check system that allowed Alexis access to military installations despite his self-described mental problems and a series of interactions with law enforcement.
Defense Secretary Chuck Hagel said Wednesday that “obviously there were a lot of red flags” — and legitimate questions about “why they didn’t get picked up.”
“Where there are gaps, we will close them,” Hagel said. “Where there are failures, we will correct them.”
Police in Rhode Island said they had no reason to arrest Alexis, or to put him under observation, after he told them about the voices. They said such run-ins are a common occurrence.
But Lt. William Fitzgerald, of the Newport, R.I., police, said his department faxed its report to the local naval police station, where an official pledged to follow up. A spokesman at Naval Station Newport declined to say whether military police did so.
“This will be part of the mix here,” Hagel said, adding that officials will be seeking answers to questions about “how we could have brought those kinds of reports into the clearance process.”
Hagel said the Pentagon is launching reviews on the granting and renewing of security clearances and on access procedures at military facilities. An independent panel will also tackle those issues. The Navy is doing its own examination.
“Obviously, something went wrong,” Hagel said. “We will review everything.”
Alexis’s encounters with federal health-care workers were also receiving scrutiny.
Law enforcement officials said Alexis went to two Veterans Affairs facilities, complaining of insomnia. Both visits were after the August incident in Rhode Island.