Boston suburbs on lockdown amid search for Boston Marathon bombing suspect

April 19, 2013: Police in tactical gear arrive on an armored police vehicle as they surround an apartment building while looking for a suspect in the Boston Marathon bombings in Watertown, Mass. (AP)

Police teams arrive in Watertown, Mass. as the manhunt for bombing suspect Dzhokhar A. Tsarnaev continues. (Fox News)

April 19, 2013: Police arrive in Watertown, Mass. as the manhunt for bombing suspect Dzhokhar A. Tsarnaev continues. (Fox News)

April 19, 2013: Police in tactical gear conduct a search for a suspect in the Boston Marathon bombings in Watertown, Mass. (AP)

April 19, 2013: Police in tactical gear surround an apartment building while looking for a suspect in the Boston Marathon bombings in Watertown, Mass. (AP)

April 19, 2013: Police prepare to go door-to-door in Watertown, Mass. as the manhunt for bombing suspect Dzhokhar A. Tsarnaev continues. (Fox News)

April 19, 2013: A police officer in tactical gear conducts a search for a suspect in the Boston Marathon bombings, in Watertown, Mass. (AP)

April 19, 2013: A woman heads away from a building in Cambridge, Mass., after being evacuated by police from her home next door. (AP)

April 19, 2013: Police conduct door-to-door searches in Watertown, Mass. as the manhunt for bombing suspect Dzhokhar A. Tsarnaev continues. (Fox News)

April 19, 2013: Police secure a perimeter around an apartment building in a neighborhood in Watertown, Mass., while searching for a suspect in the Boston Marathon bombings. (AP)

April 19, 2013: Police arrive in Watertown as town is under virtual lockdown while authorities hunt for the second suspect in the Boston Marathon bombing.  (Fox News)

April 19, 2013: A police officer runs with his weapon drawn as he conduct a search for a suspect in the Boston Marathon bombings in Watertown, Mass. (AP)

April 19, 2013: Police run with their weapons drawn as they conduct a search for a suspect in the Boston Marathon bombings in Watertown, Mass. (AP)

April 19, 2013: Police go door-to-door in Watertown, Mass. in a manhunt for bombing suspect Dzhokhar A. Tsarnaev. (Fox News)

April 19, 2013: A police officer runs with his weapon drawn as he conduct a search for a suspect in the Boston Marathon bombings in Watertown, Mass. (AP)

April 19, 2013: Police arrive in Watertown as manhunt for second bombing suspect continues. (Fox News)

April 18, 2013: A sign along I-93 in Medford, Mass. announces no MBTA service. (AP)

April 19, 2013: A barefooted woman runs for cover as police surround a home while searching for a suspect in the Boston Marathon bombings in Watertown, Mass. (AP)

April 19, 2013: Police presence grows in the neighborhoods of Watertown, Mass. as a massive search involving hundreds of heavily armed law enforcement officials continues for one of two suspects in the Boston Marathon bombing. (AP)

April 19, 2013: An unidentified resident of Norfolk Street in Cambridge, Mass., talks with police. (AP)

April 19, 2013: This photo shows police presence in Watertown as police hunt for the second suspect in the Boston Marathon bombing.  (Fox News )

April 19, 2013: Officials address the media during a news conference in Watertown, Mass. (AP)

April 19, 2013: Police secure an area near the Massachusetts Institute of Technology campus. (AP)

April 19, 2013: Officers wearing tactical gear arrive at the Watertown neighborhood of Boston. (AP)

April 19, 2013: Police officers work a crime scene in Watertown, Mass. (AP)

April 19, 2013: Police officers walk near a crime scene in Watertown, Mass. (AP)

April 19, 2013: Police officers aim their weapons in Watertown, Mass. (AP)

April 19, 2013: Police officers aim their weapons in Watertown, Mass. (AP)

April 19, 2013: Police work a crime scene in Watertown, Mass. (AP)

April 19, 2013: Police hold a man in handcuffs, who they later released, in a neighborhood of Watertown, Mass. (AP)

April 19, 2013: A police officers rides on the back of a van at a staging area as a manhunt is conducted for a suspect in Watertown, Mass. (AP)

April 19, 2013: Police officers stand ready at a crime scene in Watertown, Mass. (AP)

April 19, 2013: Police monitor areas around Boston as the manhunt for the second Boston Marathon bombing suspect continues. (Fox News )