Navy Yard shooting in Washington, D.C. (21 images)

Aaron Alexis, seen in this FBI photo, is the alleged gunman who opened fire at the Washington Naval Yard this morning killing at least 12 people, in Washington, D.C. September 16, 2013. UPI/FBI/Handout

The flag is lowered to half-mast at the White House in Washington, DC on September 16, 2013 after the shocking shooting at the Navy Yard that left at least 12 people dead. UPI/Olivier Douliery/Pool

D.C. Metropolitan Police Officers evacuate people from the Naval Yard following this morning's shooting, in Washington, D.C. on September 16, 2013. Earlier this morning a gunman opened fire inside the Naval complex killing at least 12. UPI/Kevin Dietsch

D.C. Metropolitan Police Officers work the crime scene at the Naval Yard in Washington, D.C. on September 16, 2013. Earlier this morning a gunman opened fire inside the Naval complex killing at least 12. UPI/Kevin Dietsch