The United States Navy Yard shooter Aaron Alexis had carved 'Better off this way, My Elf weapon' onto his shotgun, which he used to kill twelve people on Monday.
Investigators said they were still examining the meaning of the phrases, ABC News reports.
It is being speculated that Alexis knew he would die in his killing spree, the report added.
Although unsure about the significance of 'ELF', authorities said it could mean 'extremely low frequency' in military and technical language.
Police has still not been able to judge the reason for the 34-year-old to go on a rampage killing 12 people at the Naval Sea Systems Command on Monday, New York Daily News reports.
Alexis had earlier claimed he was suffering from post-traumatic stress disorder (PTSD) from 9/11 when he was arrested in Seattle in 2004 for shooting out at a construction worker's tires.
A Rhode Island cop said Alexis claimed he heard voices through the wall of a hotel room and was followed by three suspicious people who were using a microwave machine to send vibrations into his body to keep him awake.