Update: The second suspect, Dzhokhar Tsarnaev, was captured on Friday night. Read the story here.
A dragnet seemingly lifted from the script of a Hollywood action movie had Americans on the edge of their seats on Friday as heavily armed police swarmed Boston searching for one of two Russian-born Chechen brothers suspected in the bloody Boston Marathon bombings.
By nightfall, Dzhokhar Tsarnaev was reportedly surrounded as he hid in a boat in Watertown, a Boston bedroom community that was at the epicentre of a massive manhunt all day.
Authorities had barely wrapped up a briefing to lift a "stay indoors'' order and announce their search for the 19-year-old had been fruitless when news broke that they had him cornered. Police scurried to evacuate people, including children, from near the scene, while officials told various news outlets that they had their man.
The developments have transfixed a nation in the midst of a dreadful week as they watched the unprecedented spectacle of a beloved, bustling American city at a standstill amid the high-profile manhunt.
Watertown was the scene of a wild firefight hours earlier between police and the two brothers _ Dzhokhar and his 26-year-old brother, Tamerlan.
In a stunning chain of events, the brothers allegedly executed a security guard at a downtown university late Thursday night, hurled explosives at police during a car chase into the Boston suburbs and then engaged in the gun battle that left Tamerlan dead and Dzhokhar at large.
Among the explosives tossed at police during the firefight in suburban Watertown was another pressure-cooker bomb of the type used in the marathon blast, CBS News reported. The pressure cooker's lid apparently came loose as it was thrown, preventing its full detonation.
There was a major explosion during the gun battle, however, evident on audio and video tape of the firefight. The New York Times also reported that Tamerlan Tsarnaev may have had a homemade bomb strapped to his body when he went down in a hail of police gunfire.
Boston and its suburbs were completely locked down by Friday morning as police continued to pursue 19-year-old Dzhokhar Tsarnaev, searching door-to-door for him on 20 streets in Watertown.
Law enforcement officials told several media outlets that Tsarnaev was wounded during the firefight and sped away in the SUV, right over his wounded brother. Authorities reportedly attempted to track him by a trail of blood after he abandoned the vehicle.
Investigators said they found several pipe bombs, detonated and undetonated, plus another pressure-cooker bomb, but didn't say precisely where they'd discovered those explosives.
By late afternoon, concerns were mounting that Tsarnaev would continue to elude capture.
Col. Timothy Alben of Massachusetts state police conceded that efforts to find him had so far been "fruitless." But he vowed that police would redouble their efforts.
"My message to the suspect is to give himself up,'' he told the briefing.
Details about the two brothers, who immigrated to the U.S. about a decade ago, emerged at a fast and furious pace as family members and associates spoke openly to news media while social media disclosed a treasure trove of personal details.
An array of relatives, including their Toronto aunt, came forward to either fiercely defend the brothers or bitterly condemn them.
"I need evidence,'' Maret Tsarnaev told an impromptu news conference in west-end Toronto. "Show me evidence. I don't trust FBI, I don't trust any agency.''
An uncle, Ruslan Tsarni, was asked outside his Maryland home what would have provoked his nephews.
"Being losers,'' he replied angrily, adding that his brother had simply ``fixed cars'' to put food on the table for his family while living in America and bore no responsibility.
"Dzhokhar, if you are alive, turn yourself in, ask forgiveness from these people,'' Tsarni said to news cameras congregated on his driveway. ``You brought shame on our family, the entire Chechnya people. You put this shame on our entire ethnicity.''
The brothers' father _ Anzor Tsarnaev, now in Russia _ also urged his surviving son to give himself up, but warned the U.S. that "all hell will break loose'' if he's killed.
He told ABC News he spoke to his sons earlier this week, after the blasts at the famed Boston Marathon killed three people and injured more than 160.
"We talked about the bombing. I was worried about them,'' Anzor Tsarnaev said from Russia. He said his sons reassured him, saying: ``Everything is good, Daddy. Everything is very good.''
He added: ``If they kill my second child, I will know that it is an inside job, a hit job. The police are to blame. Someone, some organization is out to get them.''
Their New Jersey sister, meantime, said she was shocked.
"They were great people. I never would have expected it,'' Alina Tsarnaev told the New Jersey Star-Ledger outside her home. "They are smart _ I don't know what's gotten into them.''
The brothers were from Dagestan, which borders Chechnya in southern Russia, and initial reports suggest they were adrift after their parents returned to Russia.
Tamerlan, a boxer, was the subject of a photo essay entitled ``Will Box For Passport'' taken before he competed at the National Golden Gloves competition in Salt Lake City in 2010.
"I don't have a single American friend, I don't understand them,'' he said, according to the caption on one of the photos.
Chechens are Russians by citizenship but not by nationality. Famously tough fighters, they complain that Russians frequently discriminate against them.
Chechnya has been the scene of two wars between Russian forces and separatists since 1994. The conflicts kicked off an Islamic insurgency in the region.
On his page on Vkontatke _ the Russian-language equivalent of Facebook _ Dzhokar Tsarnaev, who became a U.S. citizen last Sept. 11, tells a joke.
"A car is driving down a street. In it are a Chechen, an Ingush and a Dagestani. Question: Who's behind the wheel? Answer: a cop.''
In the U.S. capital on Friday, federal counterterrorism officials were trying to determine if the brothers were part of a larger operation with accomplices still at large. They're also investigating whether they had any connections to foreign or domestic terrorist organizations.
By most accounts, Dzhokar Tsarnaev, an avid wrestler, was more popular than his older brother and had a network of friends. Some of them expressed shock at his involvement in the bombings, describing him as kind and intelligent.
Tsarnaev was a student on the University of Massachusetts' Dartmouth campus, and had a dorm room there. Two students told CBS News that they'd seen Tsarnaev on campus this week, after the bombings.
The school was evacuated on Friday as police descended upon the campus to scour his dorm room.
By noon on Friday, a sea of law enforcement officers had also surrounded the Cambridge, Mass., home where the brothers grew up and where Tamerlan was thought to have still resided. Police said they feared it could be booby-trapped with explosives and conducted a controlled explosion.
Subways and buses were shut down while Amtrak service to Boston was halted. Harvard University, Boston University, the Massachusetts Institute of Technology and Emerson University were all closed and students were told to stay inside.
Major-league baseball and hockey games were cancelled.
Tips about the identity of the brothers began pouring into the FBI soon after the agency released their images publicly, officials said.
The FBI got a huge helping hand from Jeff Bauman, the subject of the horrifying photo taken immediately after the bombing that showed him with both legs blown off below the knee.
Bauman provided a highly detailed description of one of the suspects _ even sketching him for police _ that allowed investigators to zero in on a culprit as they pored over a department store surveillance tape.
"He woke up under so much drugs, asked for a paper and pen and wrote, 'bag, saw the guy, looked right at me,''' Bauman's brother, Chris, told Bloomberg earlier this week.
Within hours of releasing their images, authorities say the Tsarnaev brothers had gunned down MIT police officer Sean Collier, 26, as he sat in his cruiser at 10:20 p.m. Collier had not drawn his weapon.
The brothers then hijacked a Mercedes SUV, holding the driver captive for a half-hour while they reportedly tried to use his cash card to get money from three bank machines. They managed to withdraw $800 at one ATM.
The man, who told police the brothers had confessed their crimes to him, was released unharmed at a gas station in Cambridge. As the suspects sped in his car toward Watertown, police gave chase as explosive devices were tossed at them out the window.