A duplex where a 19-year-old man was found dead is shown in Timberlea, Nova Scotia, on Friday. Royal Canadian Mounted Police say they foiled a plot to commit a mass shooting. Reuters/Landov hide caption

itoggle caption Reuters/Landov

A memorial at the site of the first explosion in the Boston Marathon bombing. Defense attorneys say too many people in the potential jury pool have some kind of personal connection to the case. Andrew Burton /Getty Images hide caption

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Belgian paratroopers guard outside a Jewish school in the central city of Antwerp on Saturday, a day after authorities made several arrests of alleged Islamist extremists who they say were plotting attacks. Yves Herman/Reuters/Landov hide caption

itoggle caption Yves Herman/Reuters/Landov

A photo provided by the U.S. Marshal's office shows terrorism suspect Adel Daoud, of Hillside, Ill. Daoud, a 20-year-old U.S citizen, has denied government allegations that he accepted a phony car bomb from undercover FBI agents in 2012, parked it by a Chicago bar and pressed a trigger. Uncredited/AP hide caption

itoggle caption Uncredited/AP

U.S. Army Maj. Nidal Hasan is charged with a 2009 killing spree that killed 13 people at Fort Hood in Texas. Homegrown terrorism by Muslim Americans has been growing over the past decade. HO/AFP/Getty Images hide caption

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January 2010: Muslim-Americans protest against terrorism outside a federal court building in Detroit, where "Christmas Day" bomber Umar Farouk Abdulmutallab was being arraigned. Stan Honda /AFP/Getty Images hide caption

itoggle caption Stan Honda /AFP/Getty Images