Friends and associates say ethnic Chechen brothers seemed well settled into American life.
Bafflement over Boston bombers' motivation
Boston //When they first saw the blurry image of one of the men wanted for the Boston bombing, many of those who knew Dzhokhar Tsarnaev joked that it could be him - but none thought to report it because the implication was beyond belief.
"He wasn't a loner, the complete opposite … he seemed like one of the most well-adjusted kids on the team," said Peter Payack, Dzhokhar's high school wrestling coach. "Never in a million years did we expect anything like this."
Former teachers, coaches, friends, and even the brothers' own parents, saw no indications that Dzhokhar, 19, or his brother Tamerlan, 26, were interested in, or capable of, perpetrating anything like the bombings on Monday that killed three and injured 176.
Tamerlan was killed in a shoot-out with the police overnight on Friday after a violent, chaotic chase through Boston, while Dhzokhar escaped on foot and was finally captured injured but alive nearly 24 hours later after a manhunt that paralysed the city.
The end of Boston's nightmare, however, raises more questions than it answers. Many potential explanations for the violence have emerged that rest on a constellation of anecdotes about the brothers' lives, but it remains unclear if the answers will be found in the Boston suburb of Cambridge, their family's homeland of the Caucasus, or the more likely mixture of experiences grounded in both.
"Obviously there are still many unanswered questions … why did young men who grew up and studied here as part of our communities and country resort to such violence? How did they plan and carry out these attacks, and did they receive any help?" Barack Obama said yesterday.
The brothers were born in Kyrgyzstan, their grandparents part of the Chechen diaspora expelled from their homeland by Stalin after the Second World War.
Facing discrimination, the brothers' father, Anzor Tsarnaev, moved his family to the predominantly Muslim Russian province of Dagestan in the early 2000s.
In 2002, Dzhokhar and his parents emigrated to the US and were joined two years later by Tamerlan and their two sisters.
The boys seemed to thrive in their new surroundings. Following his father's love for boxing, Tamerlan soon became a promising amateur fighter with dreams of joining the US Olympic team. He married an American girl, became a father and enrolled in Bunker Hill Community College with plans to become an engineer.
Dzhokhar was a popular student at his well-regarded public high school in Cambridge, where he was the captain of the wrestling team for two years. He was a second-year student at the University of Massachusetts Dartmouth, where he studied nursing and lived on campus, though thereare reports that he was failing most of his classes..
Postings and conversations with friends on Dhzokhar's Twitter feed revealed the normal preoccupations of young adults - sometimes profane, ironic musings about girls, school and even mundane references to Islam.
A profile attributed to him on the Russian social networking site VK lists "career and money" as his personal priority and "Islam" as his world view.
Many wonder whether his brother Tamerlan, whose life had taken turns for the worse after the brothers' parents divorced and moved separately to Dagestan, may have been radicalised in recent years.
He dropped out of college in 2009 and his boxing career was ended by back problems. His father has said Tamerlan had money problems since then.
Authorities have yet to find any links between the brothers and any foreign or domestic terrorist organisations.
His father said Tamerlan spent six months in Dagestan last year. Friends and relatives said that over the past year he had become more outwardly devout, growing a long beard and wearing clothes that may suggest a Salafist religious ideology.
Ruslan Tsarni, an uncle of the brothers, said he had a falling out with Tamerlan because of his increased religiosity. Mr Tsarni says he grew concerned about Tamerlan when he told him in 2009 that he had chosen "God's business" over work or school.
On Friday, the FBI revealed that they had interviewed Tamerlan in 2011 at the request of an unnamed foreign government.
"The request stated that it was based on information that he was a follower of radical Islam and a strong believer, and that he had changed drastically since 2010 as he prepared to leave the United States for travel to the country's region to join unspecified underground groups," the FBI said.
His father says the FBI told Tamerlan: "We know what sites you are on, we know where you are calling, we know everything about you. Everything."
A law enforcement official said yesterday the interview was requested by the Russian government.
Tamerlan eventually made the trip to Dagestan, where a violent insurgency against Russian rule has been simmering for years. But whether he became radicalised during his six months there and why a movement focused on independence from Russia would target the US is still not known.
By all accounts, Dzhokhar was deeply influenced by his brother. A cousin, Zaur Tsarnaev, said he had warned Dzhokhar about his brother "was up to no good", but Dzhokhar was "a sweet, innocent boy. I don't know how he is involved".
Some wondered whether other psychological factors could have been at play, such as feelings of alienation by immigrants who never managed to get a foothold in their new lives.
"Sometimes a person can look like they're blending into mainstream culture, and dress like they have, and go to parties and the rest of it, but they may feel like they never belonged," said Usha Tummala-Narra, an assistant professor of counselling psychology at Boston College. "That might be a critical part of the story."