(CBS News) WASHINGTON -- Sources say Aaron Alexis left behind two short phrases on the side of the shotgun used in the Washington Navy Yard massacre.
One of the messages scratched into the gun's metal reads, "Better off this way." The other is more cryptic: "My ELF weapon."
Investigators don't know what the etchings mean. "ELF" might be a reference to "extremely low frequency" radio waves used by the Navy to communicate with submarines.
It also may relate to a strange incident which happened six weeks ago in Newport, R.I.
Alexisto send "vibrations into his body." Newport investigators took a report and gave it to local Navy police. It apparently was never passed up the chain of command.
After the Newport episode, Alexis.
Government records show that on Aug. 23, Alexis visited a VA emergency room in Providence, complaining of insomnia. He received medication to help him sleep. Then five days later, on Aug. 28, he refilled the sleep aid prescription at a VA medical center in Washington.
Watch: Remembering the Navy Yard victims, below.
The Department of Veterans Affairs also revealed that Alexis was on partial disability for orthopedic issues and ringing in his ears. He received disability benefits totaling $395 a month.
His family has claimed that Alexis had also sought and received treatment for mental health issues. But the VA said it had no record of Alexis receiving that kind of care.
In a statement, the VA said "...he never sought an appointment from a mental health specialist."
The FBI still doesn't have a motive for the shootings, and investigators say that so far, they have found no clear connections between Alexis and any of his victims.