The younger one won a scholarship, excelled at wrestling, and worked as a lifeguard at Harvard University. The elder one aspired to be a professional boxer and became a father.
From the outside, the lives of Dzhokhar and Tamerlan Tsarnaev followed a familiar trajectory – an immigrant's journey, marked by notable successes and grinding struggles.
And until they allegedly placed backpacks full of explosives on their shoulders and headed to the Boston Marathon, there was nothing in their story that suggested they would turn into a deadly threat.
The search for Dzhokhar, 19, paralyzed the city of Boston for much of Friday and grew to include thousands of law enforcement personnel. By evening, authorities had taken him into custody after cornering him in a backyard in Watertown, Mass. Early in the day, his elder brother Tamerlan, 26, was killed in a shootout. The placid streets near the brothers' home in Cambridge were transformed into a scene bristling with federal agents and bomb-sniffing dogs.
For those in the neighbourhood who knew the brothers – particularly Dzhokhar – there was shock and disbelief.
He "was always so nice," said Belinda Marson, 20, who took two classes with him in high school. She described him as a "people person," who once patiently helped a teacher spell his name and pronounce it properly.
"It's just so crazy," added Dajarna Brock, 18, who remembers Dzhokhar from elementary school and high school, where they were both members of sports teams. "He was not a weird loner," she said. "He was just a quiet, happy guy."
To his father, Anzor Tsarnaev, who once worked in Boston as a car mechanic, Dzhokhar was simply "an angel."
The brothers arrived in the U.S. a decade ago from Central Asia. The family's roots are in Chechnya, a majority-Muslim Russian republic that was the site of two brutal wars between separatists and Russian forces.
Before immigrating to the U.S., the family stayed for a time in Dagestan, a Russian republic next to Chechnya that has also experienced insurgent violence for more than a decade.
Not much is known yet about their early years in Boston. By all accounts, Dzhokhar grew to become a typical teenager in America: one who loved Nutella, threw himself into athletics, and jabbered with friends in a blizzard of Tweets. ("Being bilingual is da bomb," read one from the account a classmate confirmed belonged to him.)
His high school – Cambridge Rindge & Latin School – sits next to a park and a public library and is just around the corner from the Harvard campus. The neighbourhood where he lived is one of quiet streets and steady gentrification, home to both gritty storefronts and a restaurant that calls itself a "food lab."
There is no suggestion that Dzhokhar was ill at ease with his peers; several who knew him said he had plenty of friends. He was a decorated member of the wrestling team, known for his speed and love of competition. After he graduated, he would return to the high school periodically to skirmish with younger wrestlers.
For Tamerlan, the transition to life in the U.S. wasn't as seamless. He wanted to become a professional boxer, something that never panned out. In an undated online gallery of boxing images assembled by photographer Johannes Hirn, Tamerlan is quoted as saying: "I don't have a single American friend, I don't understand them."
Still, he had a keen grasp of the bargain the country offered its immigrants. Eight years ago, in an article in the Lowell Sun about him competing in a boxing tournament, Tamerlan said: "I like the USA ... America has a lot of jobs. That's something Russia doesn't have. You have a chance to make money here if you are willing to work."
Somewhere along the way, something began to go very wrong. The two brothers' outer life – of ordinary striving and challenges – masked a more radical turn.
Their parents returned to Dagestan at some point, reportedly after their father suffered health troubles. There are reports that Dzhokhar, after excelling in high school, was getting poor grades at the University of Massachusetts Dartmouth, where he was a student.
Meanwhile, his brother Tamerlan had grown more devout in his practice of Islam in recent years, shunning alcohol and praying five times a day. Some of the videos he deemed his "favourites" on YouTube included sermons from a Lebanese-Australian preacher who has said Muslims should raise their children to be holy warriors.
Two years ago, the U.S. Federal Bureau of Investigation, at the request of a foreign country, interviewed Tamerlan about possible ties to extremist groups but found nothing of concern, according to CBS News. In 2009, the police reportedly arrested Tamerlan for an incident of domestic violence.
An uncle, Ruslan Tsarni, speculated that his nephews could have been disillusioned about life as newcomers to the U.S.
The source of their disaffection? " Being losers, hatred of those who were able to settle themselves, I can only imagine. Anything else to do with Islam is a fraud," Mr. Tsarni told journalists outside his Maryland home.
He urged Dzhokhar to "turn yourself in and ask for forgiveness."
There are still large blanks in the brothers' story, particularly its final chapters. Tamerlan travelled to Russia last year and returned to the U.S. six months later, according to U.S. officials.
Earlier this year, Tamerlan told an aunt in Toronto that he was in Dagestan visiting his father, having left his wife and child behind in Boston. But his father, Anzor, disputed that account, telling reporters that he hadn't seen his elder son in over a year.
Authorities haven't released any information on the two brothers' activities or whereabouts in the days leading up to the attack on the marathon. After the deadly explosions, Dzhokhar and Tamerlan remained in Boston, and the Twitter account believed to be used by Dzhokhar stayed active.
"I'm a stress free kind of guy," one of the last posts said, on Wednesday, two days after the bombing.
The account carries a greeting, "Salam aleikum" (Peace be upon you) and a logo of FC Anzhi Makhachkala, a soccer club in Dagestan, where Dzhokhar once lived.
For the parents of the two brothers, the news unfolding over the course of Friday has been a living nightmare. Both have publicly asserted their belief in their sons' innocence.
"I am 100 per cent sure that this is a set up," said Zubeidat Tsarnaev, who said she was the boys' mother, in an interview with Russia Today, an English-language television channel in Russia. "It is impossible for them to do such things."
The family also reportedly includes two sisters, but it is unclear how old they are or where they live.
Across Cambridge, people struggled to explain and comprehend the transformation of two men who had seemed reassuringly unremarkable.
Eddie Foster, a high school senior, used to wrestle with Mr. Tsarnaev, whom he described an extremely quick athlete and a keen competitor. "My coach loved him," he said. "He was nice to be around."
With reports from Tu Thanh Ha, Mark MacKinnon, Patrick White, and the Associated Press