Indiana Army National Guard Pvt. Trea Colon inspects her equipment during a field training exercise at Camp Atterbury and Muscatatuck. Sgt. Jeremiah Runser/U.S. Army via DVIDS hide caption

itoggle caption Sgt. Jeremiah Runser/U.S. Army via DVIDS

Spectators bow their heads during a moment of silence during a ceremony to commemorate the 20th anniversary of the Oklahoma City bombing at the Oklahoma City National Memorial, on Sunday. Sue Ogrocki/AP hide caption

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The Alfred P. Murrah Federal Building was "literally right up against the road so it was extremely vulnerable," said architect Barbara Nadel. One of the government's first responses was to close a two-block stretch of Pennsylvania Avenue in front of the White House. AFP/AFP/Getty Images hide caption

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High-definition video cameras with 30x magnification keep watch over the Boston Marathon finish line, where two bombs detonated in 2013, killing three people and injuring hundreds. Jesse Costa/WBUR hide caption

itoggle caption Jesse Costa/WBUR

Iraq's Prime Minister Haider al-Abadi, speaking Thursday in Washington, said recent battlefield victories showed the Islamic State could be defeated. The extremist group still holds large parts of the west and the north of Iraq. Kevin Wolf/Kevin Wolf hide caption

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President Obama meets Cuban President Raul Castro at the Summit of the Americas in Panama City on April 11. The White House says it wants to remove Cuba from its list of state sponsors of terrorism. Pablo Martinez Monsivais/AP hide caption

itoggle caption Pablo Martinez Monsivais/AP

"I'm very concerned about the public's respect for law enforcement officers and the safety of those they are designed to protect," House Judiciary Chairman Rep. Bob Goodlatte, seen here in 2013, told NPR. "This is a very important issue to me and one I intend to follow closely." Carolyn Kaster/AP hide caption

itoggle caption Carolyn Kaster/AP