Police in tactical gear conduct a search for a suspect in the Boston Marathon bombings, on April 19, 2013, in Watertown, Massachusetts.(AP Photo/Matt Rourke)
Police officers walk near a crime scene in Watertown, Massachusetts, on April 19, 2013. A tense night of police activity that left a university officer dead on campus just days after the Boston Marathon bombings and amid a hunt for two suspects caused officers to converge on a neighborhood outside Boston, where residents heard gunfire and explosions. (AP Photo/Matt Rourke) #
Officials search a dark area near Massachusetts Institute of Technology following reports of a shooting, on April 18, 2013, in Boston.(AP Photo/Julio Cortez) #
This photo (left) released by the FBI early Friday, April 19, 2013, shows what the FBI is calling suspect 1, in black cap, and suspect number 2, in white cap, walking through the crowd in Boston on Monday, April 15, 2013, before the explosions at the Boston Marathon. The photo at right, also released Friday, shows a suspect that officials identified as Dzhokhar Tsarnaev, being sought by police in the Boston Marathon bombings Monday. (AP Photo/Federal Bureau of Investigation) #
Officials brief the media on a standoff in Watertown, Massachusetts, on April 19, 2013. Authorities say one of two suspects in the Boston Marathon bombing is dead and a massive manhunt is underway for another in the Boston suburb of Watertown early Friday morning April 19, 2013. (AP Photo/Julio Cortez) #
Metro SWAT members hang off the back of a truck as they prepare to search the School and Walnut Street neighborhood for one remaining suspect on April 19, 2013 in Watertown, Massachusetts. (Darren McCollester/Getty Images) #
A law enforcement bomb technician walks away after preparing the controlled detonation of a suspicious object during a search for a suspect in the Boston Marathon bombing, in Watertown, on April 19, 2013. (Reuters/Lucas Jackson) #
A woman looks out a window at her home as police start to search an apartment building while looking for a suspect in the Boston Marathon bombings in Watertown, on April 19, 2013. (AP Photo/Charles Krupa) #
Police run with their weapons drawn as they conduct a search for a suspect in the Boston Marathon bombings, on April 19, 2013, in Watertown. (AP Photo/Matt Rourke) #
A neighbor is escorted to safety as police surround a home while searching for a suspect in the Boston Marathon bombings in Watertown, on April 19, 2013. (AP Photo/Charles Krupa) #
Heavily armed FBI agents, on the scene on Norfolk Street in Cambridge, Massachusetts, on April 19, 2013. Two suspects in the Boston Marathon bombing killed an MIT police officer, injured a transit officer in a firefight and threw explosive devices at police during a getaway attempt in a long night of violence that left one of them dead and another still at large Friday, authorities said as the manhunt intensified for a young man described as a dangerous terrorist. (AP Photo/Michael Dwyer) #
An MBTA transit official closes a door at Malden Center station in Malden, Massachusetts, on April 18, 2013 as area MBTA commuter trains are suspended, while police search for a suspect in the Boston Marathon bombing. (AP Photo/Elise Amendola) #
Police patrol through a neighborhood in Watertown, while searching for a suspect in the Boston Marathon bombings, on April 19, 2013. All residents of Boston were ordered to stay in their homes Friday morning as the search for the surviving suspect in the marathon bombings continued after a long night of violence that left another suspect dead. (AP Photo/Charles Krupa) #
A barefooted woman runs for cover as police surround a home while searching for a suspect in the Boston Marathon bombings in Watertown, on April 19, 2013. (AP Photo/Charles Krupa) #
A police officer evacuates a shoeless man holding a child as members of law enforcement conduct a search for a suspect in the Boston Marathon bombings, on April 19, 2013, in Watertown. (AP Photo/Matt Rourke) #
With his weapon drawn, an officer inspects dumpsters behind an apartment building in Watertown, Massachusetts, on April 19, 2013.(AP Photo/Julio Cortez) #
A police officer runs with his weapon drawn as he conduct a search for a suspect in the Boston Marathon bombings, on April 19, 2013, in Watertown. (AP Photo/Matt Rourke) #
Police in tactical gear surround an apartment building while looking for a suspect in the Boston Marathon bombings in Watertown, on April 19, 2013. All residents of Boston were ordered to stay in their homes Friday morning as the search for the surviving suspect in the marathon bombings continued after a long night of violence that left another suspect dead. (AP Photo/Charles Krupa) #
A U.S. military helicopter lands behind Watertown Mall as law enforcement agencies search for 19-year-old bombing suspect Dzhokhar A. Tsarnaev on April 19, 2013 in Watertown, Massachusetts. (Mario Tama/Getty Images) #
An empty street is seen near the historic Faneuil Hall (on left, with white cupola) and City Hall (back, center) in Boston, on April 19, 2013, as the area is under a lockdown during the manhunt for Dzhokar Tsarnaev. (Reuters/Neal Hamberg) #
SWAT officers from suburban communities aid Boston police officers in keeping guard at the nearly deserted South Station area of Boston, on April 19, 2013.(Reuters/Neal Hamberg) #
In Montgomery Village, Maryland, Ruslan Tsarni, uncle of the suspected Boston Marathon bombing suspects, speaks to reporters in front of his home, on April 19, 2013. Tsarni asked the still at large bombing suspect Dzhokhar Tsarnaev to turn himself in.(Allison Shelley/Getty Images) #
A member of the Cambridge police bomb squad deploys a robot on Norfolk Street during a search for searching a suspect in the Boston Marathon bombings in Cambridge, on April 19, 2013. (AP Photo/Michael Dwyer) #
Residents view police in tactical gear as law enforcement conduct a search for a suspect in the Boston Marathon bombings, on April 19, 2013, in Watertown.(AP Photo/Matt Rourke) #
This photo shot through a window screen provided by Samantha England, shows police in tactical gear outside England's home in Watertown, Massachusetts, on April 19, 2013. (AP Photo/Samantha England) #
A sign calling for citizens of Boston to "Shelter in Place", on I-93 in Boston, on April 18, 2013. Two suspects in the Boston Marathon bombing killed an MIT police officer, injured a transit officer in a firefight and threw explosive devices at police during their getaway attempt in a long night of violence that left one of them dead and another still at large Friday, authorities said as the manhunt intensified for a young man described as a dangerous terrorist. (AP Photo/Elise Amendola) #
Police officers search house to house for the second suspect in the Boston Marathon bombings in a neighborhood of Watertown, on April 19, 2013.(Reuters/Brian Snyder) #
A resident records the scene around Norfolk Street in Cambridge, on April 19, 2013 as authorities search for Boston Marathon bombing suspect Dzhokhar Tamerlan. (AP Photo/Michael Dwyer) #
West New York Police officers collect evidence from the apartment of Alina Tsarnaeva, sister of the Boston Marathon bombing suspects, in West New York, New Jersey, on April 19, 2013. (Reuters/Eduardo Munoz) #
Anzor Tsarnaev, who calls himself father of Dzhokhar and Tamerlan Tsarnaev, the two suspects in the Boston Marathon bombings, gives an interview in Makhachkala in this video grab from the footage via Reuters TV, on April 19, 2013. The two suspects in the Boston Marathon bombings are ethnic Chechen brothers who spent much of their lives away from the breakaway Russian republic and showed few signs of radicalism in the United States, friends and relatives say. Much is still unknown about Dzhokhar and Tamerlan Tsarnaev, Cambridge residents identified by a national security official as suspects in the twin bombings that killed three people and wounded 176 on Monday.(Reuters/Reuters TV) #
Law enforcement officers place themselves in an overhead position on Arsenal Street, in the search area for Dzhokar Tsarnaev, in Watertown, on April 19, 2013.(Reuters/Lucas Jackson) #
Members of the media take cover on the instruction of law enforcement officers while covering a police reaction to a suspect on Arsenal Street, in Watertown, on April 19, 2013. (Reuters/Lucas Jackson) #
A person watches from inside a home as a SWAT team member keeps watch while searching for 19-year-old bombing suspect Dzhokhar A. Tsarnaev, on April 19, 2013 in Watertown, Massachusetts. (Mario Tama/Getty Images) #
Police SWAT team members run towards a police assault on a house as gunfire erupts on Franklin Street during the search for Dzhokhar Tsarnaev, the surviving suspect in the Boston Marathon bombings, in Watertown, on April 19, 2013. (Reuters/Jim Bourg) #
A police SWAT team member readies his weapon in the middle of Franklin Street as gunfire erupts during the search for Dzhokhar Tsarnaev, the surviving suspect in the Boston Marathon bombings, in Watertown, on April 19, 2013. (Reuters/Jim Bourg) #
Police officers guard the entrance to Franklin street where there was an active crime scene search for the suspect in the Boston Marathon bombings, on April 19, 2013. (AP Photo/Matt Rourke) #
A light beam from a helicopter, top right, aims in the direction of Watertown, Massachusetts, where officials searched for a suspect in the Boston Marathon explosions, on April 19, 2013. (AP Photo/Julio Cortez) #
Police watch as an ambulance leaves Franklin Street at the end of the search for Dzhokhar Tsarnaev, the surviving suspect in the Boston Marathon bombings, in Watertown, on April 19, 2013. Boston Police said on Friday they have taken custody of the second suspect, Dzhokhar Tsarnaev, and are sweeping the suburban Boston neighborhood where he was captured after a massive manhunt.(Reuters/Shannon Stapleton) #
Members of different law enforcement agencies, in an area around Franklin Street in Watertown, Massachusetts, on April 19, 2013, at the end of a 22-hour manhunt. After a car chase and shootout with police, one suspect in the Boston Marathon bombing, Tamerlan Tsarnaev, 26, was shot and killed by police early morning April 19, and his brother and second suspect, 19-year-old Dzhokhar A. Tsarnaev was captured later the same night, after being found hiding inside a boat in the backyard of a Watertown residence. The two men are suspects in the bombings of the Boston Marathon on April 15 that killed three people and wounded at least 170.