Suspects Tamerlan Tsarnaev, wearing a dark baseball cap, and Dzhokhar A. Tsarnaev, behind him wearing a white baseball hat, walk among those watching the Boston Marathon. (Bob Leonard / Associated Press)
Tamerlan Tsamaev, right, fights Lamar Fenner in a boxing match during the 2009 Golden Gloves National Tournament of Champions in Salt Lake City. (Glenn DePriest / Getty Images)
Dzhokhar and Tamerlan Tsarnaev, both wearing baseball caps, at the marathon 10 to 20 minutes before the bombings. (Bob Leonard / Associated Press)
Tamerlan Tsarnaev, left, fights Lamar Fenner at the 2009 Golden Gloves National Boxing Tournament in Salt Lake City. (Rick Egan / Associated Press)
Dzhokhar A. Tsarnaev, left, poses with a friend upon graduating from Cambridge Rindge and Latin High School in Cambridge, Mass. The young man at right is the nephew of Boston radio show host Robin Young. The two have talked about their connection to the suspect on WBUR radio. (Robin Young / Associated Press)
Two photos released by the FBI show “suspects 1 and 2,” as the FBI is referring to them. They are shown walking through the crowd in Boston before the explosions at the marathon. (Associated Press)
A photo released by the Boston Police Department from a convenience store security camera shows a person believed to be Dzhokar Tsarnaev, identified as ‘Suspect 2' by the FBI. (Boston Police / EPA)
A handout photograph released by the Boston Police Department shows a person believed to be Dzhokar Tsarnaev as a child. (Boston Police / EPA)
This undated photo of Dzhokhar Tsarnaev was provided by the vKontakte website, the Russian version of Facebook. (Associated Press)
Dzhokar Tsarnaev, age 19, previously identified as Suspect 2 in the Boston Marathon bombing investigation, seen in a photo released by the FBI Friday morning. ()
A photo released by the FBI shows a man suspected in the Boston Marathon bombings that killed three people and injured about 180. (FBI)
A photo released by the FBI shows both of the suspects in the suspected in the Boston Marathon bombings that killed three people and injured about 180. (FBI)
A photo released by the FBI shows a suspects in the Boston bombings. (FBI)
A photo released by the FBI shows two men suspected in the Boston Marathon bombings that killed three people and injured about 180. ( FBI)
A photo released by the FBI captures one of two men suspected in the Boston Marathon bombings. (FBI)
A photo released by the FBI shows a man with a backpack, one of two suspects in the Boston bombings. (FBI)
A photo released by the FBI shows one of the suspects, wearing a dark hat and carrying a backpack. (FBI)
A photo released by the FBI shows the second suspect, wearing a light-colored hat and also carrying a backpack. (FBI)
A photo released by the FBI shows the second suspect in the marathon crowd. (FBI)
A photo released by the FBI captures the face of the second bombing suspect. (FBI)
