One Phrase Read: "Better Off This Way"

NEW YORK (CBSNewYork/AP) — The gunman in Monday’s Washington Navy Yard massacre left behind two short phrases etched into the side of his shotgun, sources told CBS News.

One of the messages scratched into Aaron Alexis’ gun reads: “Better off this way.” The other is more cryptic: “My ELF weapon.”

Is is unclear what “ELF” means, but investigators believe it might be a reference to “extremely low frequency” radio waves used by the Navy to communicate with submarines.

The etching may be related to an incident in Newport, R.I. in August, in which Alexis, a New York native, told police he believed people were following him and using a microwave machine to send vibrations to his body.

Police alerted officials at the Newport Naval Station about the naval defense contractor’s call, but it apparently was never passed up the chain of command.

Alexis, 34, gunned down 12 people at a Navy Yard building before being killed in a shootout with police. His motive remains a mystery.

On Wednesday, Cathleen Alexis, Aaron’s mother, made her first public comments by reading a statement from her home in Bedford-Stuyvesant, Brooklyn.

“Our son, Aaron Alexis, has murdered 12 people and wounded several others,” she said. “His actions have had a profound and everlasting effect on the families of the victims.

“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.

“To the families of the victims, I am so, so very sorry that this has happened. My heart is broken.”

Note from mother of Navy Yard shooter Aaron Alexis (pool)

Note from mother of Navy Yard shooter Aaron Alexis (pool)

She did not want to appear on camera and did not take questions from a reporter.

NYPD clergyman Bishop Dr. Gerald Seabrook met with Alexis’ mom.

“The mother is very sad, but she’s a very strong woman whose heart goes out to the victims of what happened,” he said. “Just put yourself in her position right now and image what she’s going through.”

MORE: CBS News | CBS DC | PHOTOS: Mass Shooting At Washington Navy Yard

Barry Williams, Alexis’ former boss at the Borough of Manhattan Community College, where Alexis worked from 2001-03 as a computer network technician, described the man as someone who grew frustrated with people who did not meet his expectations and was an impatient overachiever, perhaps too eager to advance.

“He’d get a grudge and would hold onto it longer than was normal. … ,” Williams told CBS 2’s Lou Young. “You look at the spectrum of humanity, and there was nothing that popped out about him that he would do something like kill 12 people.

“You never know about people. Some people, it’s obvious. But some people are borderline. And they just go through the wrong things in life and it tips them over, and then you get something like this.”

Melinda Downs said she’s struggling to reconcile how her friend is the same man who took so many innocent lives.

“It’s like Dr. Jekyll and Mr. Hyde,” she said. “Who was this guy? The guy that I knew was so honorable.”

Alexis visited two hospitals in recent weeks, complaining about insomina. The Veterans Administration insisted that he was not being treated for mental illness.

On Saturday, Alexis visited Sharpshooters Small Arms Range in Lorton, Va., about 18 miles southwest of the nation’s capital. He rented a rifle, bought bullets and took target practice at the 16-lane indoor range, then bought a shotgun and 24 shells, according to the store’s attorney.

Two days later, Alexis entered the sprawling Washington Navy Yard, a 41-acre labyrinth of buildings protected by armed guards and metal detectors where employees must show IDs to get past doors and gates.

He was equipped with his pass for base access and the shotgun. Once inside, Alexis picked a handgun off an officer and, armed with two weapons, terrorized the building’s occupants.

The Navy said he obtained his security clearance when he enlisted in the Navy reserves in 2007, which was good for 10 years and remained valid after he left the service in 2011.

During his time of active service, the Navy said Alexis had incidents of insubordination, disorderly conduct and being absent from work without authorization, but nothing that gave commanders any clue he was capable of such violence.

Alexis also had run-ins with the law over shooting incidents.

In 2004, he was arrested in Seattle for allegedly shooting out the tires of another man’s vehicle. He was arrested again in 2010 for discharging a firearm into the ceiling of his Fort Worth, Texas apartment.

Aaron Alexis mug shot (credit: Fort Worth Police)

Aaron Alexis mug shot (credit: Fort Worth Police)

After the shooting incident in 2004, Alexis told police he was present during “the tragic events of September 11, 2001″ and described “how those events had disturbed him.”

Detectives later spoke with Alexis’ father, who lived in New York at the time. He told police Alexis had anger management problems associated with PTSD and that Alexis had been an active participant in rescue attempts on 9/11.

In response to the shooting, Defense Secretary Chuck Hagel ordered the Pentagon on Wednesday to review the physical security of all U.S. defense facilities worldwide and the security clearances that allow access to them.

“Obviously, when you go back in hindsight and look at all of this, there were some red flags,” said Hagel. “Of course there were. And should we have picked them up? Why didn’t we? How could we? All those questions need to be answered.”

Hagel is also tasking an independent panel to undertake the same reviews. He said Wednesday that “where there are gaps, we will close them.”

According to CBS News, a new report released by the Pentagon inspector general found that 52 felons had routine access to military installations, which put “military personnel dependents, civilians and installations at an increased security risk.”

CBS News’ John Miller reported that the felons who received access included “drug dealers” and “alleged child molesters.”

The White House said Wednesday that President Barack Obama will attend a memorial service Sunday for the victims of the mass shooting.

Details about where and when the memorial will take place have not been announced.

At a White House event, first lady Michelle Obama expressed her “sincere heartbreak over Monday’s tragedy.”

She said, “The men and women who lost their lives devoted their careers to protecting our country.”

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