At a press conference held just moments ago, FBI spokesperson Valerie Parlave confirmed that they believe the 34-year-old shooter behind Monday's mass shooting at the U.S. Navy Yard in D.C., identified as Aaron Alexis, acted alone. Parlave added that because of that fact, the investigation into the incident has moved into the "evidence recovery and information gathering" stage.

It's believed that Alexis entered Building 197 with a shotgun, Parlave said, adding that there's no information to suggest that Aaron had an AR-15 in his possession at the time of entry. Alexis may have gained access to an additional handgun once he was inside the building and after he began shooting. The FBI confirmed that Alexis had legitimate access to the Navy Yard and utilized a valid pass to gain entry. 

In fielding questions from the press, Parlave reiterated that Alexis obtained the handgun through a lawful purchase made in Virginia and that the shooter arrived in the Washington, D.C. area on or about August 25. He resided at local hotels since that point, most recently staying at a Residence Inn in Southwest Washington, D.C. starting September 7. 

The investigation into Alexis's motive spans across the U.S. to cities he inhabited before moving to the nation's capitol. Parlave emphasized that no piece of information contributed by the public is too small and urged residents to send any and all tips to the FBI by calling 1-800-CALLFBI.