Authorities gave no indication of what they might believe the brothers' motivations could have been in the crime.
Tamerlan Tsarnaev, the dead suspect, studied at a local community college and was a Golden Gloves boxer. He also reportedly had a wife and young child. The FBI questioned him two years ago at the request of the Russian government, but found nothing suspicious, according to the AP.
Dzhokhar Tsarnaev, who was remembered by former classmates as bright and personable, posted links to pro-Chechnyan independence sites on his social media page, and listed his "world view" as Islam.
Tsarnaev appeared to be posting to his Twitter account even after the marathon attacks, writing in his last post on wednesday, "i'm a stress free kind of guy". His posts covered everything from cute photos of his cat to rap lyrics.
In an interview with The New York Times, the suspects' father said Tamerlan had been unable to become a U.S. citizen because he was arrested for hitting his girlfriend, and that he traveled to Russia last year to live for six months and renew his passport. Dzhokhar is a naturalized U.S. citizen.
The suspects' uncle, when told that one of his nephews was killed by the local CBS News stationFriday afternoon, replied that he deserved it. “He deserved his. He absolutely deserved his,” Ruslan Tsarni said. “They do not deserve to live on this earth.”
Later, in an emotional press conference outside his home in Maryland, Tsarni said his nephews had brought shame upon his family, and called them "losers." He speculated that they were not "able to settle themselves" and were "angry at everyone who was able to." He said he did not believe they were motivated by radical politics in Chechnya or religion.
He added that he hadn't been in touch with the family for several years but would not say why. Other family members, including an aunt and the brothers' father, said they did not believe the brothers could have planted bombs.
The University of Massachusetts at Dartmouth announced shortly after 10:30 a.m. on Friday that they were evacuating the entire campus after learning Tsarnaev is a registered student there. The suspect reportedly attended a party there on Wednesday night, two days after the bombing.
Earlier, at sunrise Friday, Gov. Patrick ordered a shutdown of all public transit and for residents in the city of Boston and on its edges to stay indoors. Amtrak also shut down all trains between Boston and New York.
Boston and the surrounding areas of Watertown, Waltham, Belmont, Cambridge, Newton, Allston and Brighton were placed on lockdown for most of Friday. A no-fly zone was declared over Watertown. The city of Boston was eerily quiet for much of the day, the city's busy intersections totally abandoned.
The mayhem began at approximately 10:20 p.m. Thursday in Cambridge when police said the bombing suspects shot and killed an MIT campus officer, Sean Collier, 26. Davis said that Collier was "assassinated" by the suspects while sitting in his cruiser. The terror suspects then carjacked a Mercedes-Benz SUV with the driver inside and fled, eventually letting the driver go unharmed.
The suspects were then spotted in Watertown, where federal agents swarmed in. At approximately 3:30 a.m., Massachusetts State.
Police issued a plea on Twitter for residents of Watertown to lock their doors and not open them for anyone, as dozens of police officers, many of them off duty, searched backyards and exteriors of houses there, and a police perimeter of several blocks was established.
Worried residents were also told to turn off their cell phones out of fear that they could trigger improvised explosive devices.
The suspects exchanged dozens of rounds of gunfire with patrol officers, and lobbed IEDs out of their vehicle, injuring several officers.
Tamerlan Tsarnaev was shot by police and brought to Beth Israel Medical Center. He arrived at the hospital under cardiac arrest with multiple gunshot wounds and blast-like injuries to his chest. The second suspect fled on foot.
A transit police officer, Richard H. Donohue, was seriously wounded during the exchange of gunfire, officials said.
K9 units and SWAT teams searched homes on Spruce Street as officers with a police robot searched an SUV that the suspects had abandoned. Multiple devices were left in the road and two handguns were recovered, according to police scanners.
"We believe this to be a terrorist," said Boston Police Commissioner Ed Davis, of Tsarnaev. "We believe this to be a man who has come here to kill people. We need to get him into custody."
Police in Watertown, Newton, Brighton and Cambridge were put on high alert. "Units use caution," an officer said. "He might have an explosive object on his person."
Police were able to track down images of the suspects after a victim of the attacks, Jeff Bauman, came to them with a description, Bloomberg reported Thursday. Bauman's legs were torn apart by the bomb.
