Update (7:08pm): NBC News - The Boston Marathon bombing suspect was captured Friday night after police found him in a boat in a suburban backyard following a bloody rampage and daylong manhunt, law enforcement sources said.
Cheers went up from a crowd of police gathered at the scene in Watertown, Mass., where bursts of gunfire had been heard over the course of two hours.
The dramatic turn of events ended five days of terror from the bombing at the marathon finish line, which killed three people, wounded 176 and left the city of Boston on edge.
Update (5:47pm): NBC News: Suspect #2 is alive and in custody. About to be tended to by medics.
The sound of gunfire erupted in a Boston suburb Friday evening, less than an hour after police said residents could leave their homes even though the marathon bombing suspect was still on the run despite an all-day, door-to-door search.
Federal officials were told someone was found in a boat in the yard of a home, but there was no word on whether it was accused bomber Dzhokhar Tsarnaev, 19, sources told NBC News.
About an hour after the first barrage in Watertown, Mass., two more bursts of shots were heard.
Dozens of police and armored vehicles were in the area, where residents had been told to take shelter.
The dramatic turn of events came less than an hour after Massachusetts State Police Col. Timothy Alben told a press conference that Tsarnaev had probably not left the state but nevertheless lifted a lockdown order that had been in effect since before dawn.
Police had just released new details about the scope of a bloody overnight rampage that began with the death of a campus security officer and ended with the death of Tsarnaev's 26-year-old brother, Tamerlan, with a bomb strapped to his body.
Hours after the FBI put out their photos Thursday night, the brothers exchanged 200 rounds with police during a stunning pre-dawn firefight and left behind seven homemade explosives, officials said.
The violence led to 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 looking for the younger suspect.
Investigators chased leads all day but could not find the suspect, a naturalized U.S. citizen of Chechen origin who grew up in Cambridge after his family moved here a deacde ago, seeking asylum.
“There is still a very, very dangerous individual at large," said Massachusetts Gov. Deval Patrick said Friday night.
Still, officials said residents could venture outside and the subway system was going back on line. They said patrols would be beefed up in Watertown, where the suspect was last seen, but state police tactical units were pulling back.
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.
It was a rapid turn of events after a night of violence that police said included the slaying of a Massachusetts Institute of Technology patrol officer in his car in Cambridge, a carjacking and a half-hour hell ride for a man who was eventually released unharmed, before the gun battle with police.
The drama began at MIT 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.
Tips about the identity of the suspects were still pouring in when the Tsarnaev brothers fatally shot campus 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.
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.
The suspects' uncle, Ruslan Tsarni, called the brothers "losers" and urged Dzhokhar to turn himself in.
"We're ashamed," he thundered outside his Maryland home.
The frantic search for the alleged bomber left streets across the Boston area eerily quiet. 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.
The lockdown initially affected more than 300,000 people in Cambridge, Watertown, Newton, Brighton, Allston and Belmont, but by 8 a.m., the entire city of Boston was paralyzed.
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.
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. "We believe this to be a man who's come here to kill people."