Former Arizona Rep. Gabrielle Giffords, accompanied by her husband, retired astronaut Mark Kelly, speaks during a news conference in Manchester, N.H., in July. They were there to encourage state political leaders to have courage in the fight to expand background checks on gun purchases. Mary Schwalm/AP hide caption

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President Obama speaks during a memorial service at the Marine Barracks Sunday in Washington, D.C., honoring victims of Monday's shooting at the Navy Yard. Brendan Smialowski/AFP/Getty Images hide caption

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Police say Aaron Alexis, who was killed Monday, gunned down 12 people at the Washington Navy Yard. FBI/Reuters/Landov hide caption

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At the White House and around the nation, flags are flying at half-staff since Monday's mass shooting at the Washington Navy Yard. Olivier Douliery /UPI/Landov hide caption

itoggle caption Olivier Douliery /UPI/Landov

Aaron Alexis, whom the FBI believes to have been responsible for the shootings at the Washington Navy Yard in Washington, D.C., is shown in this handout photo released by the FBI on Monday. FBI/Reuters/Landov hide caption

itoggle caption FBI/Reuters/Landov

In Herkimer, N.Y., police and suspect Kurt Myers were in a standoff from midday Wednesday into early early Thursday. Overnight, these officers were on the town's North Main Street. Brett Carlsen/Getty Images hide caption

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