The break came around nightfall when a homeowner in Watertown saw blood on his boat, pulled back the tarp and saw a bloody Dzhokhar Tsarnaev hiding inside, police said. After an exchange of gunfire, he was seized and taken away in an ambulance.
Raucous celebrations erupted in and around Boston, with chants of "USA! USA!" Residents flooded the streets in relief four days after the two pressure-cooker bombs packed with nails and other shrapnel went off.
During the long night of violence leading up to the capture, the Tsarnaev brothers killed a Massachusetts Institute of Technology police officer, severely wounded another lawman and took part in a furious shootout and car chase in which they hurled homemade explosives at police, authorities said.
Watertown Police Chief Edward Deveau said one of the explosives was the same type used during Monday's Boston Marathon attack, and authorities later recovered a pressure cooker lid that had embedded in a car down the street. He said the suspects also tossed two grenades before Tamerlan Tsarnaev ran out of ammunition and police tackled him.
But while handcuffing him, officers had to dive out of the way as Dzhokhar drove the carjacked Mercedes at them, Deveau said. The sport utility vehicle dragged Tamerlan's body down the block, he said. Police initially tracked the escaped suspect by a blood trail he left behind a house after he abandoned the Mercedes, negotiating his surrender hours later.
The federal Bureau of Alcohol, Tobacco, Firearms and Explosives is tracing the weapons to try to determine how they were obtained by the suspects.
Chechnya, where the Tsarnaev family has roots, has been the scene of two wars between Russian forces and separatists since 1994. That spawned an Islamic insurgency that has carried out deadly bombings in Russia and the region, although not in the West.
Investigators have not offered a motive for the Boston attack. But in interviews with officials and those who knew the Tsarnaevs, a picture has emerged of the older one as someone embittered toward the U.S., increasingly vehement in his Muslim faith and influential over his younger brother.
The Russian FSB intelligence service told the FBI in 2011 about information that Tamerlan Tsarnaev was a follower of radical Islam, two law enforcement officials said Saturday.
According to an FBI news release, a foreign government said that Tamerlan Tsarnaev appeared to be a strong believer and that he had changed drastically since 2010 as he prepared to leave the U.S. for travel to a region in Russia to join unspecified underground groups.
The FBI did not name the foreign government, but the two officials said it was Russia. The officials spoke on condition of anonymity because they were not authorized to talk about the matter publicly.
The FBI said that in response, its agents interviewed Tamerlan Tsarnaev and relatives, and did not find any domestic or foreign terrorism activity. The bureau said it looked into such things as his telephone and online activity, his travels and his associations with others.
An uncle of the Tsarnaev brothers said he had a falling-out with Tamerlan over the man's increased commitment to Islam.
Ruslan Tsarni from Maryland said Tamerlan told him in a 2009 phone conversation that he had chosen "God's business" over work or school. Tsarni said he then contacted a family friend who told him Tsarnaev had been influenced by a recent convert to Islam.
Tsarni said his relationship with his nephew basically ended after that call.
As for Dzhokhar Tsarnaev, "he's been absolutely wasted by his older brother. I mean, he used him. He used him for whatever he's done," Tsarni said.
Albrecht Ammon, a downstairs-apartment neighbor of Tamerlan Tsarnaev in Cambridge, said in an interview that the older brother had strong political views about the United States. Ammon quoted Tsarnaev as saying that the U.S. uses the Bible as "an excuse for invading other countries."
Tamerlan Tsarnaev studied accounting as a part-time student at Bunker Hill Community College in Boston for three semesters from 2006 to 2008, the school said. He was married with a young daughter.
Dzhokhar Tsarnaev was a student at the University of Massachusetts-Dartmouth. The college was evacuated Friday, but officials said residence and dining halls will reopen Sunday.