Updated 8:23 p.m. ET
BOSTONPolice responded en masse Friday evening after shots were fired in the town were a Boston Marathon bombing suspect was last seen. A man hiding in a boat behind a house has been surrounded and authorities are approaching the situation cautiously.
Boston Mayor Thomas Menino said Dzhokhar A. Tsarnaev, 19, of Cambridge, Mass., the at-large suspect in the Boston Marathon bombing, is the man in the boat, although that is yet to be confirmed by law enforcement.
Shortly after the lockdown was lifted early Friday evening in the town where the at-large Marathon bombing suspect was last seen, journalists reported several shots could be heard. Later Friday evening, reporters said several explosions could also be heard at the scene.
Police are approaching the scene cautiously because authorities believe Tsarnaev may have explosive devices.
Police say Tsarnaev escaped on foot early Friday after escaping a gun battle in which explosives were lobbed at police and in which his older brother, also a suspect in the Marathon bombing, was killed.
Tsarnaev has so far evaded a furious police manhunt that effectively shut down the city of Boston Friday.
Prior to the gun battle in Watertown, Mass., in which a police officer was critically wounded, the two suspects killed an MIT police officer, then hijacked a car.
Federal sources believe the suspect who is still alive is either wearing an explosive vest, or has explosives with him, reports national security correspondent Bob Orr.
Boston Police Commissioner Edward Davis says the suspect at large is the one seen in the white hat in images of the Boston Marathon suspects released by the FBI Thursday. Davis says he is "armed and dangerous."
At a press briefing late Friday afternoon Col. Timothy Alben of the Massachusetts State Police said investigators have completed a sweep of the 20-block interior of Watertown.
"We do not have an apprehension o our suspect this afternoon, but we will have one. We're committed to that," said Alben.
Mass. Gov. Deval Patrick, who has earlier imposed a "stay-indoors" order for the city, said this afternoon that the order has been lifted, but he asked the public to remain vigilant.
Police evacuated residents in Cambridge who lived on the same block as one of the suspects, in whose house several homemade bombs were discovered by police.
"These are pipe bombs with internal threads and caps on either end, with standard fuses - [not] very sophisticated stuff, but dangerous stuff," CBS News senior correspondent John Miller said.
Beginning early Friday residents throughout the Boston area -- including Watertown, Cambridge, Waltham, Newton and Belmont -- were advised to keep their doors locked and not let anyone in. The Boston Police Department warned residents to "stay home." Vehicles were barred from entering or leaving Watertown.
Universities throughout Boston were closed; public transit, bus line and taxi service was suspended, as was Amtrak service was also suspended indefinitely between Boston and New York. The FAA has also imposed temporary flight restrictions in the Boston area. Logan International Airport is open but is operating under heightened security. JetBlue is allowing anybody scheduled to fly to or from Boston to change their ticket for free.
The Boston Red Sox announced that. The Boston Bruins (who were to play the Pittsburgh Penguins this evening) likewise have postponed tonight's game.
Suspects of Chechnyan origin
The suspects were identified by law enforcement officials and family members as ethnic Chechen brothers from Dagestan, which neighbors Chechnya in southern Russia. They lived near Boston, and had been in the U.S. for about a decade after receiving asylum, an uncle said.
The two have been identified as Dzhokhar A. Tsarnaev, 19, of Cambridge, Mass., and his brother, Tamerlan Tsarnaev, 26. They are legal permanent residents of the U.S.
CBS News confirmed that Dzhokhar is an American citizen, having been naturalized on September 11, 2012.
He is reportedly a student at the University of Massachusetts Dartmouth and lived in a dorm there. Correspondent Anthony Mason reports that Tsarnaev was seen on campus yesterday afternoon where he spoke with a friend, who said there was nothing out of the ordinary in their conversation.
Tamerlan -- the suspect seen in FBI photos released Thursday as wearing the black hat -- was wounded in an exchange of gunfire with police during last night's pursuit. He was captured and rushed to Beth Israel Deaconess Medical Center in Boston, where he died at 1:35 a.m. Doctors said he had gunshot wounds and a blast injury. The wounds were throughout the trunk of the man's body, CBS Station WBZ reported.
Ruslan Tsarni, an uncle of the suspects, told CBS Station WBZ "it absolutely devastated me," upon learning that his nephews had been named a suspect in the Marathon bombing. "It's not comprehendable, in our family."
Alvi Tsarni, another uncle of the suspects, told CBS News said he was shocked about learning news of his nephews. "It's not possible. My nephews can't do this stuff, there's no way," he said.
In Toronto, the suspects' aunt, Maret Tsarnev, told the CBC she was in disbelief after seeing the FBI's wanted photos this morning. "This cannot be true," she said. "If somebody wants to convince me, show me evidence. . . . I am suspicious this was staged -- this picture was staged," she said.
Gun battle in Watertown
The MIT shooting on the Cambridge campus Thursday night was followed by gunfire and explosions in Watertown, about 10 miles west of Boston.
John Miller reports that the evening's events began with the robbery of a 7-Eleven convenience store in Cambridge. It was originally reported that the two suspects were involved in the robbery; however, a spokeswoman for the Cambridge 7-Eleven on Massachusetts Avenue told CBS News that the robbery was unrelated.
Nonetheless, when an MIT police cruiser responding to a disturbance call entered the area, the suspects apparently feared they were being targeted.
"They encounter an MIT Police Officer, and rather than see, 'Is he going to follow us? Is he going to chase us?' it appears that they came up and engaged him, killed him in his police vehicle, took off," said Miller.
The MIT officer who had been responding to report of a disturbance Thursday night was ambushed and shot multiple times, according to a statement from the Middlesex district attorney's office and Cambridge police.
The officer, who was later pronounced dead at Massachusetts General Hospital, was identified as 26-year-old Sean Collier.
The Middlesex district attorney's office said Collier was a Somerville resident who had worked at MIT since January 2012. Before that, he was a civilian employee of the Somerville Police Department.
Authorities said after the shooting, the two men rode off in a stolen police vehicle, then carjacked a man in a Mercedes-Benz, keeping him with them in the car for half an hour before releasing him at a gas station in Cambridge. The man, who was not injured, informed police of the carjackers.
The search for the vehicle led to a chase that ended in Watertown, where authorities said the suspects threw explosive devices from the car and exchanged gunfire with police at about 1 a.m. Friday. Dozens of police officers and FBI agents were in the neighborhood and a helicopter circled overhead.
A transit police officer was seriously injured during the chase, authorities said.
Officer Richard Donohue, Jr., 33, was rushed to Mount Auburn Hospital in Cambridge, where he is in critical condition, reports WBZ.