In a chaotic, violent overnight that began with a robbery, the fatal shooting of a MIT police officer and a stolen car chase, police officers traced Boston marathon bombing suspects from Cambridge to Watertown, amid reports of further gunfire and explosions. During the chase, one suspect was killed, according to police, and a second remains at large. "We believe this to be a terrorist," Boston Police Commissioner Ed Davis said. (See photos of the search as it continued through Friday.)
Robin Young shared this photo of her nephew, right, and Dzhokhar Tsarnaev on left, happy Cambridge Rindge and Latin grads. (Robin Young/WBUR)This combination of photos provided on Friday, April 19, 2013 by the Federal Bureau of Investigation, left, and the Boston Regional Intelligence Center, right, shows a suspect that officials have identified as Dzhokhar Tsarnaev, being sought by police in connection with Monday's Boston Marathon bombings. (AP Photo/FBI, BRIC)Amtrak police bomb sniffing dogs checking stranded passengers near South Station at about 9:30 a.m. Friday morning. (Steve Brown/WBUR)Law enforcement officials stand guard while searching for an individual believed to be involved in the Boston Marathon explosions in Watertown, Mass., Friday, April 19, 2013. (AP Photo/Julio Cortez)Police in tactical gear surround an apartment building while looking for a suspect in the Boston Marathon bombings in Watertown, Mass., Friday, April 19, 2013. (AP Photo/Charles Krupa)A neighbor is escorted to safety as police surround a home while searching for a suspect in the Boston Marathon bombings in Watertown, Mass., Friday, April 19, 2013. (AP Photo/Charles Krupa)This undated photo provided by the Middlesex District Attorney's Office shows Massachusetts Institute of Technology Police Officer Sean Collier, 26, of Somerville, Mass., who was shot to death Thursday, April 18, 2013 on the school campus in Cambridge, Mass. Authorities said surveillance tape recorded late Thursday showed one of the Boston Marathon bombing suspects during a robbery of a nearby convenience store before Collier was shot to death while responding to a report of a disturbance. (AP Photo/Middlesex District Attorney's Office)Black bunting is hung at MIT police headquarters in Cambridge, Friday April 18, 2013. (Fred Thys/WBUR)Boston Police move in to search an apartment building on Melendy Ave in Watertown. (Jesse Costa/WBUR)Mt. Auburn St. closed at Arlington St. Friday April 19, 2013. (Jesse Costa/WBUR)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., Friday, April 19, 2013. (AP Photo/Charles Krupa)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, Mass., Friday, 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 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/Charles Krupa)Police in tactical gear surround an apartment building while looking for a suspect in the Boston Marathon bombings in Watertown, Mass., Friday, April 19, 2013. (AP Photo/Charles Krupa)
This video appears to have been taken by a Watertown resident of a shootout in Watertown overnight:
A photo of police activity in the Watertown area, posted at 7:32 a.m. April 19, 2013. Photo by John Peck / WBURPolice perimeter near Vassar and Main street in Cambridge, near the MIT building 32 Stata Center Thursday night/early Friday morning. (Joe Spurr/WBUR)A police officers rides on the back of a van at a staging area as a manhunt is conducted for a suspect Friday, April 19, 2013, in Watertown, Mass. One of two suspects in the Boston Marathon bombing is dead and a massive manhunt is underway for another, authorities said early Friday April 19, 2013. Residents of Watertown, a Boston suburb, have been advised to keep their doors locked and not let anyone in. (AP Photo/Matt Rourke)Officials brief the media on a standoff in Watertown, Mass., Friday, 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)From overnight, police at Vassar and Main street in Cambridge, near the MIT building. Photo by Joe Spurr / WBUR
