Peter Foster and Tom Parfitt try to piece together the background events that turned two young men into terror suspects - and discover that those who knew them are shocked.
He married into a world of carports and clapboard houses that for so many immigrants embodies the American dream, and yet even as he did so, Tamerlan Tsarnaev was apparently preparing to destroy what he had once heralded as a great gift.
Until the terrible events unfolded in Boston last week, for the Russell family of Rhode Island the 26-year-old suspected bomber was not a terrorist but the man who married their daughter Katherine, then 21, converted her to Islam and gave her a child.
Like all of America, the family struggled yesterday to make sense of how - as Barack Obama put it in his address to the nation - two young men who grew up and studied in America, "as part of our communities and our country", could resort to such violence.
The Russell family had no answers. "We cannot begin to comprehend how this horrible tragedy occurred," said a family statement delivered through a half-opened front door. "In the aftermath of the Patriots' Day horror, we know that we never really knew Tamerlan Tsarnaev."
Perhaps his wife or younger brother Dzhokhar, 19, who was still in a serious condition in hospital yesterday - will provide some of the answers.
Getting to know Tamerlan - as the FBI spelled his name - and Dzhokhar and unravelling their journey from grateful, wide-eyed immigrants to the point where they were able to murder and maim is the urgent task of investigators.
The barest facts are these. Their lives began in war-torn Chechnya, but in the 90s, the family moved to Kazakhstan and then to neighbouring Dagestan, where the boys attended School No 1 in the capital, Makhachkala.
By 2003, when Tamerlan was in his early teens, and Dzhokhar was 8, the boys moved to the United States as refugees, settling in Massachusetts where their father worked as a car mechanic, training his athletic young sons in boxing and martial arts. Ten years later, they would become the Boston bombers.
Piece by piece the information is emerging, each scrap of testimony arriving like brushstrokes on a canvas that will take many months of work for the police and the FBI to build up until something as close as possible to the truth emerges.
In 2004, after winning a "Golden Gloves" amateur boxing competition in nearby Lowell, Massachusetts, Tamerlan, then 14, was full of praise for his new home. "I like the USA ... America has a lot of jobs. That's something Russia doesn't have," he told his local newspaper. "You have a chance to make money here if you are willing to work."
John Allan, owner of Wai Kru Mixed Martial Arts Boston where Tamerlan trained, remembers - at least in those early days - a respectful, disciplined young man, and a brilliant fighter.
"He was the best boxer in Boston. He smoked all the professionals," Allan told the Boston Globe, adding that the boy's father, Anzor, had done a good job with his son. "They were an incredible family," he said. "This was so shocking to me."
"In the ring, he could knock a man out with one punch," Gene McCarthy, founder of the Somerville Boxing Club, told the Boston Globe. "But when he sat at a piano, he could play classical music like you wouldn't believe. The [person] I knew was a sweetheart."
Both went to high school at Cambridge Rindge and Latin, a state school in Massachusetts known for being ethnically diverse and for having the actors Matt Damon and Ben Affleck, and the poet ee cummings, among alumni.
It was a far cry from sparse but well-scrubbed School No 1 in Makhachkala where the boys studied from September 2001 to March 2002. The Sunday Telegraph visited it yesterday, seeing children seated at low desks, reading and singing a song to their teacher. Asked by the director Magomed Davudov what things they should never do, a 6-year-old girl replied: "You should never kill someone, and you should look after nature."
It is in recollections from their American high school that the temperamental differences between the two brothers begin to emerge.
Tamerlan concentrated on his boxing, aspiring to compete in the Olympics and to fight for the US rather than Russia. There were, though, clear indications he was failing to fit into American life.
From 2006 to 2008, Tamerlan enrolled for three semesters on a part-time accounting course at Bunker Hill Community College in Boston but, again, he didn't seem to fit in. "He wasn't even close" to getting a degree, according to a spokesman for the college.
"I don't have a single American friend. I don't understand them," Tamerlan told an interviewer in 2009 before another boxing competition, lamenting the breakdown of "values" in America and voicing worries about the excesses of American life, observing "people can't control themselves".
Pictures from the time show a young man in love with himself, if not the world around him.
On the way to the gym, he poses in front of his Mercedes car in brilliant-white moccasins, black trousers, carrying the accessories - from sunglasses to smartphone - that young Americans dream of. But in the avalanche of recollections and testimony, there appears to be few prepared to testify to something good about him.
The contrast with Dzhokhar was stark. Perhaps because he had arrived in the US at a younger age, he showed no such signs of difficulty settling down, being remembered by school and university friends as a gregarious, fun-loving character who spoke accentless English, enjoyed socialising and was a leader on the school wrestling team.
He was one of 45 high-school seniors to receive a US$2500 scholarship from the city of Cambridge, and classmates remember a popular, all-American boy who wore a tuxedo and red bowtie to his senior prom.
"He was happy to be there, and people were happy he was there," Sierra Schwartz, 20, told the New York Times. "He was accepted and very well liked."
"Everything about him was wonderful," said Larry Aaronson, a retired history teacher at Cambridge Rindge and Latin School. "He was outgoing, very engaged, he loved the school. He was grateful not to be in Chechnya."
That sunny disposition seems to have continued until the end, with dorm-mates at the University of Massachusetts, Dartmouth, recalling that as late as last Thursday - when he attended a soccer team party - he was the same easy-going college kid. Unlike his older brother, Dzhokhar also had the occasional cigarette and a girlfriend off-campus who is believed to be among three people questioned by police. "He was nice. He was cool. I'm just in shock," said 19-year-old Florida Addy, who lived in his dorm.
Around 2009 the edges of the picture start to darken, particularly for Tamerlan. His aunt Maret Tsarnaeva, who lives in Toronto, said she noticed a change, particularly in Tamerlan's attitude to religion. "He was not devout, practising. But about three years ago he began praying five times a day," she said.
At around this time, Tamerlan met Katherine Russell, a 21-year-old first-year student at Suffolk University in Boston who became his girlfriend, and later wife. They would often be seen walking in the Rhode Island neighbourhood with their baby at weekends. Neighbours said Katherine Tsarnaev had converted to Islam and would dress in loose-fitting clothing and wear a veil over her hair, in keeping with Islamic traditions. Paula Gillette, 51, told the Sunday Telegraph of the delight of Katherine Tsarnaev's parents father, Warren who is a doctor, and her mother, Judith, a nurse, at the arrival of their granddaughter Zahara, now 3. "They were so happy to have a granddaughter. This is terrible for them."
The website spotcrime.com reported Tamerlan was arrested for domestic violence in July 2009 after assaulting a woman. His cousin Zaur Tsarnaev, 26, made similar allegations about Tamerlan, drawing the contrast with his "sweet innocent" brother Dzhokhar.
"He was always getting into trouble. He was never happy, never cheering, never smiling. He used to strike his girlfriend," Zaur told the Boston Globe from the Dagestani capital, adding, "I used to warn Dzhokhar that Tamerlan was up to no good."
As recently as 2011, there were still no signs - even to trained eyes - that the brothers were moving towards violent jihadist beliefs.
That year, the FBI admits it interviewed Tamerlan "at the request of a foreign government" - understood to be the Russians - but reportedly found no "derogatory" information on the young man, and therefore, as one official put it, the matter was "put to bed". Dzhokhar worked as a lifeguard at Harvard University where the man who hired him, George McMasters, was an ex-marine who says he interrogated prisoners in Guantanamo Bay for the National Guard in 2003 and 2004. "It is surreal for me, considering I have been dealing with these guys for 10 years," McMasters, 56, said, recalling the respectful young man he hired. "And then I come home, and they are in my backyard, in my pool."
One acquaintance of Dzhokhar who emailed the blog of Andrew Sullivan, speculated he had fallen under his brother's influence. "My feeling is that the reason that [Dzhokhar] was involved has entirely to do with his brother ... Given that his brother essentially raised him, I think this is an awful case of evil being perpetuated because of the trust and love [Dzhokhar] had for his brother."
Latterly, there were some signs - not that the brothers were preparing to commit the bombings - but indications that something fundamental had changed.
After a seven-month stay in Russia last year, a "lost" period that investigators will now be scrutinising minutely, the YouTube channel bearing Tamerlan's name began to feature jihadist materials.
There was a rant by the Australian jihadist cleric (and ex-boxer) Feiz Muhammad and one featuring the Millenarian prophecy, cited by al-Qaeda-linked groups of the Black Banners of Khurasan, that dreams of the time when an Islamic force will purify Central Asia.
Whatever triggered Tamerlan's radicalisation, family friends in the Dagestani capital yesterday said it was not his parents, Anzor and Zubeidat, who seemed to have had as much difficulty processing their two sons' transformation as many of their friends.
"The family had nothing to do with the wahhabis," said Vyacheslav Kazakevich, 36, a neighbour, referring to the conservative Muslims linked to the Islamist insurgency that operates from the forests outside Makhachkala. "Anzor is a hard worker who does favours for people. He owns a perfume shop and he wanted to open another one here."
By September 1 last year, just 10 days before Dzhokhar became a US citizen, there were signs the happy-go-lucky younger brother had also become infected with his brother's anti-American feelings. 'Idk [I don't know] why it's hard for many of you to accept that 9/11 was an inside job, I mean I guess f*** the facts y'all are some real #patriots #gethip," he wrote on his Facebook page.
Later he would taunt America over al-Qaeda's most successful terror attack, "Sept 10th baby, you know what tomorrow is. Party at my house!"
Albrecht Ammon, 18, who lived directly below the flat shared by the brothers, said he recently saw Tamerlan in a pizzeria, where they argued about religion and US foreign policy.
Tsarnaev argued that many US wars are based on the Bible, used as "an excuse for invading other countries". But even then he added he had nothing against the American people.
Whatever finally emerges as the underlying cause which persuaded the two young men to launch their murderous attacks - a sense of alienation, jihadi motivation or obsession forged in the midst of their fraternal relationship or a combination of all three - by Saturday Tamerlan would be dead and Dzhokhar surrounded in the town of Watertown.
Only a week ago, Allan, the owner of the martial arts centre where Tamerlan trained, received an email saying after two years away, the once respectful boy had come back to the gym, but now he was being rude, and walking on the mats with his shoes.
With hindsight, said Allan, "it was a clear indication that something was up".
Tragically for Boston and the four innocent people who lost their lives after two bombs tore through the crowds watching the annual marathon, no one had foresaw quite what.
- Telegraph Group Ltd, Observer, AP