Aaron Alexis, the man police believe went on a shooting rampage at the Navy Yard in Washington, D.C. and killed 12 people, carved messages into the guns he used for the massacre, ABC News reports.
He died in a shootout with police on Monday.
Alexis carved "BETTER OFF THIS WAY" into one of the guns and "MY E-L-F WEAPON" into another, sources told ABC.
Authorities speculate that "E-L-F" might stand for "extremely low frequency," according to ABC. This is significant because told Rhode Island police last month that he was hearing voices of three people and that they were "sending vibrations into his body" with "some sort of microwave machine."
It wasn't the first time he'd had a brush with the law. Alexis apparently had a history of mental illness.
In 2010, his neighbor called police after a gun discharged in Alexis' apartment and shot a bullet hole through her floor, and in 2004, he was arrested for shooting out the tires on a man's vehicle. He told police that he was in a rage-induced blackout at the time of the 2004 incident.
Alexis might have been suffering from Post Traumatic Stress Disorder. He's originally from New York City, and his father told police that he directly participated in the rescue attempts after the 9/11 attacks.
Officials still aren't sure of Alexis' motive for the Navy Yard shooting. He reportedly had clearance to enter the facility.