Kerry Sanders reports from the scene as police activity escalates after gunfire was heard.
By Pete Williams, Richard Esposito, Michael Isikoff and Tracy Connor, NBC NewsThe Boston Marathon bombing suspect was captured wounded but alive Friday night after police found him in a boat in a suburban backyard following a bloody rampage and a daylong manhunt, law enforcement sources said.
The arrest of Dzhokhar Tsarnaev, 19, ended five days of terror from the double bombing at the marathon finish line, which killed three people, wounded 176 and left the city of Boston on edge.
"We got him," Boston Mayor Tom Menino tweeted.
"CAPTURED!!! The hunt is over. The search is done. The terror is over. And justice has won," the Boston Police Department said on its Twitter account.
Cops cheered as the suspect was taken into custody in Watertown, Mass. just before 9 p.m., and residents flooded the streets, some chanting, "USA!"
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Police cornered Tsarnaev around 7 p.m., less than an hour after residents were told a stay-indoors order had been lifted.
Officials said a woman in the area reported seeing blood leading to a boat in her yard, and thermal imaging from helicopters had located someone in the vessel.
A barrage of gunfire was heard and after night fell, more rounds of shots rang out. The police threw flash-bang grenades designed to disorient and brought a negotiator to the scene.
Just before 9 p.m., Tsarnaev was taken into custody and police said he had been wounded. "He sustained significant blood loss," a law enforcement official at the scene said.
As an ambulance took the suspect to the hospital, people lining the streets applauded in joy and relief.
Tsarnaev's apprehension capped a manhunt that had the city of Boston and its suburbs on total lockdown -- following a rampage that included the slaying of a campus security officer, a carjacking and the death of Tsarnaev's 26-year-old brother, Tamerlan, in a firefight with cops.
The overnight violence had triggered an extraordinary shutdown of transportation, schools and businesses in Boston and its surrounding suburbs, with police warning more than a million people to hunker down behind locked doors while SWAT teams fanned out.
The brothers' bloody last stand began about five hours after the FBI released surveillance photos of two "extremely dangerous" men suspected of planting two bombs near the finish line of Monday's Boston Marathon, killing three and wounding 176.
Read more: Who are the brothers accused of the Boston Marathon bombing?
Police are at the Cambridge, Massachusetts, home of the Boston Marathon bombing suspects, haven't yet entered the building, suspecting it may be booby-trapped. NBC's Ron Allen reports.
Tips about the identity of the suspects were still pouring in when the Tsarnaev brothers fatally shot Massachusetts Institute of Technology officer Sean Collier, 26, in his vehicle at 10:20 p.m., law enforcement officials said.
The brothers then carjacked a Mercedes SUV, holding the driver captive for a half-hour while they tried to use his cash card to get money from three ATM's, a source said. At the first, they put in the wrong number; at the second, they took out $800 and at the third, they were told they had exceeded the withdrawal limit, the source said.
The carjacking victim was released unharmed at a gas station in Cambridge, sources said. He told police the brothers said they were the marathon bombers and had just killed a campus officer.
As the duo sped in his car toward Watertown, a police chase ensued and they tossed explosive devices out the window, officials said.
There was a long exchange of gunfire, according to Andrew Kitzenberg of Watertown, who took photos of the clash from his window and shared them via social media.
“They were also utilizing bombs, which sounded and looked like grenades, while engaging in the gunfight,” he told NBC News in an interview. “They also had what looked like a pressure-cooker bomb.
“I saw them light this bomb. They threw it towards the officers,” he said. “There was smoke that covered our entire street.”
A transit officer, identified as Richard H. Donahue, 33, was seriously injured during the pursuit. Authorities said he underwent surgery at Mount Auburn Hospital.
Kitzenberg said he saw the firefight end when Tamerlan Tsarnaev ran toward the officers and ultimately fell to the ground.
Tamerlan -- the man in the black hat from FBI photos released six hours earlier -- had an improvised explosive device strapped to his chest, law enforcement officials said.
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Dzhokhar -- the brother who was wearing a white hat in the surveillance photos from the marathon -- got away when he drove the SUV through a line of police officers at the end of the street, Kitzenberg said.
Law enforcement sources told NBC News that blood found at the scene suggests Dzhokhar may have been wounded in the gun battle. The FBI released more photos of him, including a surveillance camera photo from a convenience store where the brothers had stopped for gas.
A stay-indoors order was issued for Boston and its surrounding suburbs, affecting more than a million people who were warned to lock their doors. Subways and buses were shut down, and Amtrak service to Boston was cut. The Red Sox and Boston Bruins' home games were canceled.
Harvard University, Boston University, the Massachusetts Institute of Technology and Emerson University were closed. The University of Massachusetts' Dartmouth campus was evacuated because of a possible tie to someone in the case, the school said.
Watertown was the epicenter of the search. Frightened residents were trapped inside as convoys of heavily armed officers and troops arrived by the hour and snipers perched on rooftops and in backyards.
Investigators searched all day for Tsarnaev, but with no sign of him as night approached, they said residents could venture outside. People began leaving their homes, some of them cheering.
SWAT units were still on the scene when the shots were heard just before 7 p.m. and police converged on the boat.
Amid the search, Dzhokhar's father, in Russia, told The Associated Press he was "a true angel" and described him as a medical student who was expected to visit for the holidays.
Authorities painted a starkly different picture.
"We believe this man to be a terrorist," Boston Police Commissioner Ed Davis said early in the day. "We believe this to be a man who's come here to kill people."
NBC News' Jonathan Dienst and Kasie Hunt contributed to this story.
