Alexis, 34, went on a shooting rampage at the Navy Yard on September 16, 2013, killing 12 and wounding four before officers shot and killed the former Navy reservist.
In a photo gallery released by the FBI, messages etched on the side of Alexis' shotgun are clearly visible. Carved on the left side of the shotgun are the phrases "Better of this way!" and "My ELF weapon!" while the right side says "Not what y'all say." An etching on the barrel of the shotgun says "End to the torment!"
FBI investigators believe that Alexis had a delusional belief that he was being controlled by extremely low frequency waves, and believe that the "ELF" carved on the shotgun refers to these electromagnetic waves.
According the FBI, Alexis used his legitimate security access to enter the building to carry out a massacre that lasted for roughly an hour. The FBI believes Alexis used both the shotgun and a Beretta handgun the he obtained during the course of the shooting.