Source: Aaron Alexis carved phrases into his shotgun

Cryptic phrases were carved into the Remington shotgun used by Aaron Alexis in his Monday rampage at the Washington Navy Yard, where he killed 12 people, a federal law enforcement source said Wednesday.

"Better off this way" and "My ELF weapon" were found on the wooden stock, phrases that mystified investigators but could be clues into Alexis' mindset, the source said. "Maybe that's his version of a suicide note," the source said of the first phrase.

As for ELF, "nothing is being discounted" on its meaning, the law enforcement source said.

Alexis, 34, a former Navy reservist and military subcontractor who worked on computers, had a history of mental issues and gun incidents, but was able to get a midlevel security clearance after passing background checks. He had been working for more than a week at the Navy Yard when he opened fire there Monday before being fatally shot by police.

Details on the gun and his history emerged the same day federal officials vowed to prevent another invasion of a military facility and Alexis' mother apologized in her first public statement.

Cathleen Alexis said she could not fathom her son's actions -- but is glad he can no longer harm anyone else. "Our son, Aaron Alexis, has murdered 12 people and wounded several others," she read from a statement from the living room of her Bedford-Stuyvesant apartment.

"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."

Flanked by two bishops from the Brooklyn Clergy-NYPD Task Force, the mother choked up as she read. She did not take reporters' questions.

Defense Secretary Chuck Hagel blamed security failures Wednesday and said he had ordered reviews of physical security and access procedures at military facilities and also on practices to grant and renew security passes. An independent panel will also look at those issues, he said at a Pentagon news conference. "Why they didn't get incorporated into the clearance process, what he was doing -- those are all legitimate questions that we're going to be dealing with. How do we fix it?" Hagel said.

Alexis was working at the Navy Yard as part of his second stint with a Hewlett-Packard subcontractor, The Experts, a Florida-based computer and information services provider.

He fixed computers at workstations in different cities, the company said, and he was a productive and friendly employee with a sterling record.

Alexis worked there from September to December 2012, when he quit, telling his employer he was going back to school, a company spokesman said.

He returned in June, and, like the first time, was screened by the company and the Defense Department, company officials said. He also passed vetting for an access card to a military facility, they said.

When he was rehired, The Experts found only a minor traffic violation on his record, the company said in a statement.

But in 2004, he was accused of malicious mischief in Seattle, where police said he shot the tires of a construction worker's car with a handgun, a case that was never prosecuted. In 2010, he was arrested, accused of shooting into a neighbor's home, but charges were dropped after he told authorities his gun accidentally fired as he cleaned it.

Then on Aug. 7, Alexis told police in Newport, R.I., he was hearing voices that kept him awake and that people following him were "sending vibrations into his body," according to a police report.

Alexis then visited Veterans Affairs hospitals in Rhode Island on Aug. 23 and in Washington, D.C., on Aug. 28 to obtain pills for his insomnia, the U.S. Veterans Affairs Department said in a statement Wednesday. He was alert and, when asked, denied he was struggling with anxiety and depression. He also said he did not have any thoughts about harming himself or others, veterans officials said.