A shooting at the Washington Navy Yard has left at least 12 people dead and 8 or more injured Monday morning in Washington, D.C.

Photo: twitter.com

Shots were first fired this morning at 8:20 in the Naval Sea Systems Command Headquarters building on the base.

Police say a lone gunmen, in fatigues, opened fire in a building where approximately 3,000 people work. We would learn by Monday afternoon that Aaron Alexis, 34, who was an ex-naval reservist most recently working as a contractor.

The names of seven of the victims were released late Monday: Michael Arnold, 59; Sylvia Frasier, 53; Kathy Gaarde, 62; John Roger Johnson, 73; Frank Kohler, 50; Kenneth Bernard Proctor, 46; and Vishnu Pandit, 61.

The base along with several businesses and schools throughout the Washington area were on lockdown throughout the day on Monday.

Police once thought there were accomplices to the shooting, but now feel confident that Alexis worked alone.

@USNavy posted several updates throughout the day on Monday.