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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #

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. #