This image from a surveillance video helped investigators identify Tamerlan Tsarnaev (in black cap) and his brother, Dzhokhar (in white cap), as the main suspects in the Boston Marathon bombings. FBI.gov hide caption

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Tamerlan Tsarnaev, as seen in a video taken on April 15 near the finish line of the Boston Marathon. FBI.gov hide caption

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In Boston's Copley Square on Wednesday, people gathered at a makeshift memorial to those killed and injured in the April 15 marathon bombings. Mario Tama/Getty Images hide caption

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A Massachusetts state trooper salutes Wednesday during the memorial service for Massachusetts Institute of Technology (MIT) police officer Sean Collier on the school's campus in Cambridge, Mass. Brian Snyder /Reuters /Landov hide caption

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Dzhokhar (at left) and Tamerlan Tsarnaev allegedly killed an MIT police officer, carjacked a vehicle and engaged in a gun battle with police soon after authorities distributed this image of the brothers walking near the finish line of the Boston Marathon just before two bombs exploded. Tamerlan, 26, died from injuries he received. Dzhokhar, 19, was captured Friday night. FBI.gov hide caption

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Sen. Chuck Schumer, D-N.Y. (right), talks during a hearing at which he angered Sen. Chuck Grassley, R-Iowa (far left). Grassley thought Schumer was accusing him of using the Boston bombings as an excuse to slow or kill the immigration overhaul. J. Scott Applewhite/AP hide caption

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This combination of undated photos shows Tamerlan Tsarnaev, 26, left, and Dzhokhar Tsarnaev, 19. The FBI says the two brothers and suspects in the Boston Marathon bombing. Uncredited/ASSOCIATED PRESS/The Lowell Sun & Robin Young hide caption

itoggle caption Uncredited/ASSOCIATED PRESS/The Lowell Sun & Robin Young

A sign reading "Flying With Angels Krystle Campbell," is seen Monday as a passing MBTA bus with "Boston Strong" displayed on its message board drives through Medford, Mass. A funeral service for Campbell, one of the three people killed in the marathon bombings, was held later in the day. C.J. Gunther /EPA /LANDOV hide caption

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Police officers guard the entrance to Franklin Street in Watertown, Mass., where Boston Police say they have captured the second suspect in the marathon bombings. Matt Rourke/AP hide caption

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