Federal Bureau Of Investigation

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This photo provided by the Federal Bureau of Investigation shows Timothy Virts. Police searched Thursday for an 11-year-old girl who was reported missing after her mother was found slain in their home in Dundalk. Baltimore County Police believe the girl, Caitlyn Virts, is with her father, 38-year-old Virts, and they are concerned for her safety, department spokeswoman Elise Armacost said. (AP Photo/Federal Bureau of Investigation)

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This combination of images released by the FBI on Thursday, April 18, 2013, show two images taken from surveillance video of Dzhokhar (left) and Tamerlan Tsarnaev (right) as they walk near each other through the crowd before the explosions at the Boston Marathon on Monday, April 15, 2013. (AP Photo/FBI)

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Old Enemy: Osama bin Laden told an FBI source in 1993 that he was looking to finance terrorist attacks on U.S. soil. (Associated Press)

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This photo provided by the FBI shows Robert J. Shields Jr., the newest head of the FBI's Milwaukee office. Shields arrived in Milwaukee on Monday, Feb. 24, 2014, as the office's latest special agent in charge. He replaces Teresa Carlson, who was sent to Washington last year for a temporary duty assignment that was later made permanent. (AP Photo/FBI)