Last Updated 6:18 p.m. ET
BOSTON The city of Boston was kept in virtual lockdown Friday as law enforcement engaged in a massive sweep for one of two suspects in the Boston Marathon bombing who escaped during a police pursuit early this morning. The second suspect was killed in a firefight in which explosives were lobbed at police.
During a long night of violence, the two suspects killed an MIT police officer, injured a transit officer in a vicious gun battle, and threw explosive devices at police during their getaway attempt.
The suspect who is the subject of the manhunt has been identified as Dzhokhar A. Tsarnaev, 19, of Cambridge, Mass. The second suspect, killed early this morning, was his brother, 26-year-old Tamerlan Tsarnaev.
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."
Police evacuated residents in Cambridge who lived on the same block as one of the suspects, going door-to-door telling people to leave. Police told CBS News it is just a precaution, but they have roped off the area and residents were seen coming out with suitcases.
Swarms of police surrounded various buildings as they searched for the suspect as helicopters buzzed overhead. SWAT teams, FBI agents and armored vehicles assembled at the scene as law enforcement began a sweep of the neighborhood.
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.
Alben also said there would be a controlled explosion at a house that was secured by police but deemed unsafe for investigators to search, after several homemade bombs were discovered by police.
CBS News senior correspondent John Miller said police found not just the materials to make explosives, but a number of pipe bombs already assembled. "These are pipe bombs with internal threads and caps on either end, with standard fuses - [not] very sophisticated stuff, but dangerous stuff," Miller said. He reported that IEDs were also found along the suspects' chase route.
The Middlesex district attorney said the two men are suspected of killing a Massachusetts Institute of Technology police officer on campus late Thursday, then stealing a car at gunpoint and later releasing its driver unharmed. Hours earlier, police had released photos of the marathon bombing suspects and asked for the public's help finding them.
Authorities say the suspects threw explosives from the car as police followed it into Watertown. The suspects and police exchanged gunfire, and one of the suspects was critically injured and later died while the other escaped.
Boston in lockdown
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.
Public and private schools and universities throughout Boston were closed.
Public transit service in Boston were suspended. Taxis were suspended in the morning, but were resumed in the afternoon. Amtrak service was also suspended indefinitely between Boston and New York. Peter Pan Bus Lines has suspended service to Boston, and Megabus has canceled buses between Boston and other cities.
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.
Connecticut State Police issued an alert saying they were investigating information that the suspect may be in a 1995 gray Honda Odyssey with Massachusetts plates 93NN73. The State Police had earlier issued advisors for two other cars, including one registered to the dead suspect; those cars were later located.
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 suspects, Dzhokhar and Tamerlan Tsarnaev, 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.
State police spokesman David Procopio said, "The incident in Watertown did involve what we believe to be explosive devices possibly, potentially, being used against the police officers."
During the gunfight, according to sources, Tamerlan Tsarnaev threw a bomb toward police who advanced on him. Tsarnaev was shot down.
His brother, Dzhokhar, then got back into the car to escape, backing over his brother's body in the process.
Five blocks away, Dzhokhar hopped out of the car and fled on foot.
Officer Richard Donohue, Jr., 33, was rushed to Mount Auburn Hospital in Cambridge, where he is in critical condition, reports WBZ.
President Barack Obama, who has received briefings from his national security team and counterintelligence officials on the developments in Boston throughout the day, called Massachusetts Gov. Deval Patrick and Boston Mayor Thomas Menino to pledge the government's full support in the investigation into the Boston Marathon bombing. Mr. Obama also expressed his condolences over the death of the MIT police officer killed overnight, the White House reported.