Scary new video footage released by the FBI Wednesday shows Washington Navy Yard shooter Aaron Alexis in the moments before his deadly rampage, entering the facility in his car and stalking through hallways and staircases armed with a shotgun.
The brief video shows the man creeping down staircases and crouched over as he passes through hallways on the morning of Sept. 16 bearing the firearm, the FBI said.
The shotgun carried by Alexis had messages etched into it including “End to the torment,” “Not what yall say” and “Better off this way,” the FBI said at a press conference on Wednesday.
A fourth cryptic inscription — "My ELF weapon" — might have referred to extremely low frequency electromagnetic waves, according to the FBI.
Those waves are used by the Navy to communicate with submarines, according to investigators, and the FBI said on Wednesday that electronic media recovered in their investigation indicated that Alexis might have thought he was subject to assaults from the technology.
“Ultra low frequency attack is what I’ve been subject to for the last three months, and to be perfectly honest that is what has driven me to this,” said an electronic document left by Alexis and retrieved by the FBI, according to investigators.
Alexis, a former petty officer, died after a shootout with officers at the Naval Sea Systems Command headquarters. He killed 12 people and injured four more after he opened fire with a shotgun before law enforcement officers located him on the building’s third floor and put an end to the shooting, according to officials.
The Remington 870 shotgun that officials say he used in the shooting had purple duct tape wrapped around the butt and had been bought at a gun store in Northern Virginia on Sept. 14, according to the FBI. He bought a hacksaw and other items on the same day, the FBI said on Wednesday.
Alexis also used a Beretta handgun that he obtained during the shooting, according to the FBI.
Alexis does not seem to have expected to make out it out of the Navy Yards alive, Valerie Parlave, the assistant director of the FBI Washington Field Office said, “and that he accepted death as the inevitable consequence of his actions.”
A civilian contractor who had once served as a Navy reservist, the 34-year-old was working for a Hewlett Packard Enterprises subcontractor at the time of the shooting, the company said in a statement. His military disciplinary record included instances of disorderly conduct, insubordination, and unexcused absences.
He had been involved in at least two prior incidents that involved guns. In 2004, Alexis was accused of shooting out the wheels of a vehicle in Seattle. Six years later, he allegedly fired a shot into a Fort Worth, Texas, apartment.
The shooter’s mother, Cathleen Alexis, last week apologized to the families of the victims in a statement, and said she struggled to understand her son’s actions.
“His actions have had a profound and everlasting effect on the families of the victims,” the mother said. “I don’t know why he did what he did, and I’ll never be able to ask him why. Aaron is now in a place where he can no longer do harm to anyone, and for that I am glad.”
The Department of Veterans Affairs has said that Alexis had sought out treatment for insomnia but was not treated for mental illness. He “never sought an appointment from a mental health specialist, and had previously either canceled or failed to show up for primary care appointments and claims evaluations examinations he had scheduled at VA medical centers,” the department said in a statement.
Investigators have not identified an individual or group of people who might have been the prime target, if there was one, in the mass shooting.
NBC News’ Michael Isikoff, Jim Miklaszewski, Pete Williams, Jonathan Dienst, Erin McClam, Jason Cumming, Richard Esposito, Charles Hadlock, Kyle Eppler, Jeff Black, Tracy Connor, Ali Weinberg, Courtney Kube and Andrew Rafferty contributed to this report.