WASHINGTON D.C. - NBC has confirmed the name of the suspect in Monday morning's Navy Yard shooting as 34-year-old Aaron Alexis.
Alexis is said to be originally from Fort Worth, Tex., and was a full-time Navy reservist until he left the service in 2011.
The gunman is suspected to have used the ID of a former worker to gain access to the building.
The shooting left 13 people dead, including the gunman, and as many as 10 people wounded. D.C. police have also said they are investigating the possibility of two shooters still at large.
"I heard three shots, pow, pow, pow. Thirty seconds later I heard four more shots and a couple of us that were in the cafeteria knew they were shots and started panicking and then we were trying to decide which way we were going to run out," one witness said.
President Obama said he is mourning "yet another mass shooting" and called it a "cowardly act."
There is no indication yet of a motive.