Washington Navy Yard shooting

This image taken from security cameras and released by the FBI shows Washington Navy Yard shooter Aaron Alexis moving through the hallways of Building #197 carrying a Remington 870 shotgun.  (FBI / AFP/Getty Images)

A security camera image, released by the FBI, shows Washington Navy Yard shooter Aaron Alexis moving through the hallways of Building #197.  (FBI / AFP/Getty Images)

American flags surrounding the Washington Monument fly at half-mast after the deadly shooting at the Washington Navy Yard.  (J. Scott Applewhite / Associated Press)

A wreath stands at the U.S. Navy Memorial in Washington, D.C., after a ceremony to honor the victims of the Navy Yard shootings.  (Jim Watson / AFP/Getty Images)

An armed officer with the Department of Defense works near the gate at the Washington Navy Yard, closed to all but essential personnel.  (Jacquelyn Martin / Associated Press)

Secretary of Defense Chuck Hagel, far right, gathers with Navy personnel during a ceremony at the U.S. Navy Memorial to honor the victims of the Navy Yard shooting.  (Drew Angerer / Getty Images)

A flag at the U.S. Capitol is lowered to half staff to honor the victims of today’s shooting at the Washington Navy Yard.  (Mark Wilson / Getty Images)

Restaurant owner Oui Suthamtewakul, right, and Micheal Ritrovato speak about working with Aaron Alexis, who was once employed by Suthamtewakul in Fort Worth, Texas.  (LM Otero / Associated Press)

A woman wrapped in a Red Cross blanket leaves a gathering point for reuniting family members of Navy Yard employees that was set up inside Nationals Park in the wake of the shooting.  (Win McNamee / Getty Images)

This image released by the FBI shows a photo of Aaron Alexis, who police believe was a gunman at the Washington Navy Yard shooting.  (FBI / Associated Press)

An empty Nationals Park after the Navy Yard shooting. A scheduled game between the Nationals and Atlanta Braves has been postponed by the shooting.  (Patrick McDermott / Getty Images)

Washington, D.C., Mayor Vincent Gray speaks to the media near the scene of a shooting spree at the Washington Navy Yard.  (Jim Lo Scalzo / EPA)

A Capitol police officer patrols the steps at the Capitol as the investigation continues at the nearby Washington Navy Yard.  (J. Scott Applewhite / Associated Press)

U.S. Capitol police keep watch at the East Plaza of the Capitol after the shootings at the nearby Washington Navy Yard.   (J. Scott Applewhite / Associated Press)

Speaking at the White House, President Obama discusses the Washington Navy Yard shootings, calling the victims “patriots.”  (Carolyn Kaster / Associated Press)

Office workers are evacuated from the scene of the Washington Navy Yard shootings.  (Shawn Thew / EPA)

District of Columbia Mayor Vincent Gray addresses the media on a shooting rampage at the Washington Navy Yard.   (Mandel Ngan / AFP/Getty Images)

A helicopter lifts a person off a roof at the Navy Yard.  (Saul Loeb / AFP/Getty Images)

A U.S. Park police helicopter takes a man from the scene of the Washington Navy Yard shooting.  (Jacquelyn Martin / Associated Press)

Washington police respond to the report of a shooting Monday morning at the Navy Yard in Washington, D.C.  (Saul Loeb / AFP/Getty Images)

Law enforcement officers patrol the scene of a shooting at the Washington Navy Yard.  (Saul Loeb / AFP/Getty Images)

A police officer trains his rifle on the Navy Yard building.   (Alex Wong / Getty Images)

Several emergency vehicles gathered outside the Navy Yard shooting site.   (Saul Loeb / AFP/Getty Images)