Katherine Russell Tsarnaev exits a car at the home of her parents in North Kingstown in this photograph taken on April 21, 2013.

Boston -

As America struggles to make sense of what drove two young immigrant men to carry out the Boston Marathon bombing, it may be that the only person who can provide the answers is a young American woman in a leopard-print hijab.

The descent of Tamerlan Tsarnaev, the older brother and suspected mastermind of a plot that killed three and left more than 180 injured, into Islamic extremism and alienation from his new homeland will not surprise those who have followed the roots of similar outrages in Britain.

More remarkable was the fact that the man who confided online that “I don’t have a single American friend... I don’t understand them”, and who berated his US-loving lawyer uncle as an “infidel”, had married a woman who couldn’t have been more different to the burka-clad Muslim women of his native Chechnya.

Katherine Russell, now 24 and the mother of his three-year-old daughter, Zahara, is - or rather was - a classic all-American girl from suburban Rhode Island who had dreamed of joining the Peace Corps (a US government programme in which Americans do voluntary work in developing countries) and making the world a better place. Dressed in dowdy, figure-hiding black clothes with her attractive features, dark eyes and long chestnut hair hidden under a hijab, she has tried to remain in the shadows since the attack last Monday.

But with her husband dead and her 19-year-old brother-in-law Dzhokhar Tsarnaev badly injured in hospital, FBI investigators will be determined to ask questions of Katherine, particularly regarding whether the pair acted alone and whether they had any other attacks planned.

On Monday, police said Dzhokhar is answering questions from his bed at the Beth Israel Deaconess Medical Centre via hand-written notes. He is said to have revealed details about unexploded bombs and whether he and his brother had accomplices.

The medical student, 19, cannot speak after apparently shooting himself in the throat in a bungled suicide bid. He is also thought to have bullet wounds in his head, legs and a hand.

Prosecutors charged him on Monday night with using a weapon of mass destruction and “malicious destruction of property”. The federal charges authorise penalties including death, life in prison or a term in prison. Police sources told the Daily Mail that investigators were looking into the possibility the brothers had a suicide pact so that neither of them could be put on trial.

This could explain why Dzhokhar ran over his brother in a stolen Mercedes 4x4 as he fled from the police, sources added.

Right up to his death in a hail of bullets and under the wheels of that Mercedes in Watertown last Friday, Tamerlan Tsarnaev and his wife had been very much a couple, Katherine’s lawyer confirmed on Monday - contradicting initial reports that they had become estranged.

Indeed, while her 26-year-old college dropout husband spent his days at home supposedly caring for their daughter, Zahara, Katherine was the sole bread winner - working 70 to 80 hours a week as a home health care aide.

Investigators now believe Tsarnaev was spending his days in rather more sinister activities than toddler duty.

Katherine was also living with Tsarnaev in 2011 when he made a six-month trip to the strife-torn Russian republic of Dagestan where investigators believe he may have been radicalised by jihadists.

Even neighbours in Cambridge, home of Harvard University and just across the Charles River from Boston, noticed a marked change when a year ago he grew a “Taliban-style” beard which he shaved off just a month ago. Did she not see any change? The FBI will want to know.

But the young wife who shared a small apartment with her husband claims she saw nothing amiss in the months leading up to the worst attack on the US since September 11.

Lawyer Amato DeLuca said on Monday she had not suspected her husband of anything and there was no reason for her to have done.

“When this was allegedly going on, she was working, and had been working all week to support her family,” he said.

DeLuca said his client only discovered her husband was a suspect in the bombings when she saw it on TV.

She says Dzhokhar was away at university and she didn’t see him at all at the apartment they shared with the brothers’ mother Zubeidat, who is currently in Dagestan.

How long the hard-working wife can stay out of the intense investigation into the outrage remains to be seen.

On Sunday evening, federal investigators made three visits to the family home of her parents, Dr Warren Russell and wife Judith, in the quiet suburban neighbourhood of North Kingstown, Rhode Island.

It is the same three-bedroom house (now on the market for $467 000) where the young couple spent many weekends with their daughter, the Russells’ only grandchild.

Katherine’s lawyer arrived through a back entrance to meet the investigators and later admitted that he, rather than his client, had talked to them. “We’re deciding what we want to do and how we want to approach this,” he said.

His client’s case has obvious parallels with that of Samantha Lewthwaite, the so-called “white widow” of the 7/7 King’s Cross suicide bomber Germaine Lindsay.

The unlikely Muslim convert from Aylesbury, Buckinghamshire, and Lindsay met first at an anti-Iraq War rally, but the future Mrs Tsarnaev met her husband when friends introduced them in a nightclub. She was then a student at Suffolk University in Boston although she soon dropped out. Friends say this was the influence of the controlling Tsarnaev.

They began an on-off relationship and married three years ago after she gave birth to their daughter.

Raised a Christian, she converted to Islam after their marriage. Asked why, her lawyer said: “She believes in the tenets of Islam and of the Qur’an. She believes in God.”

Her transformation startled everyone who knew the old “Katie”. School records and the stunned reaction of old friends provide an insight into the sort of woman she once was. She was the eldest of three daughters born to Warren Russell, an accident and emergency doctor, and Judith, a nurse.

At North Kingstown High School, she listed her personal motto as “Do something about it or stop complaining” and encouraged friends to “lighten up and enjoy the small things” in life.

Arty, she was keen on playing the saxophone and drawing, as well as being a member of the dance team. “I remember from our conversations that she was very intelligent,” said her former art teacher, Amos Trout Paine.

“She would definitely add to discussions in the class.”

She took part in the school’s Mismatch/Bad Hair day, dressed up for Hawaiian day and won an art award for a picture of a cat attacking a mouse in a ballet shoe.

Asked for her graduation yearbook to provide a quotation, she chose a somewhat morbid one from a David Bowie song which ends: “Knowledge comes from death’s release”.

Friends say her life changed dramatically after she met Tsarnaev. Those who knew the brothers believe Tsarnaev manipulated the younger Dzhokhar and it appears he was equally controlling with his wife.

“She was just this All-American girl who was brainwashed by her super-religious husband,” said a school friend.

“None of us would have dreamed that she would marry so young or drop out of college and have a baby or convert or be part of any of what’s happened.”

Another said: “The thing that’s so shocking is that there was nothing at all that made Katherine different. Her parents are nice people, her sisters are great. But she met this guy and everything changed.”

It is not clear from police records whether Katherine was the unnamed girlfriend who rang police, “crying hysterically”, in July 2009 to say he had beaten her up.

The woman had been yelling at Tsarnaev “because of another girl” and Tsarnaev, a champion boxer, told police: “Yes, I slapped her.”

Neighbours said they often heard ferocious screaming matches between a man and a woman in the apartment.

Apart from a furtive weekend mission, wearing a leopard print hijab, to collect a pet cat and two bags of belongings from the home she shared with Tsarnaev in Cambridge, Katherine is now hiding away in her childhood home where her family has said nothing beyond a brief statement claiming that they now “know that we never really knew Tamerlan Tsarnaev”.

With the FBI anxious to question her, the widow could claim spousal privilege and refuse to co-operate.

But as legal experts warned, if the authorities have evidence she knew anything of her husband’s intent, she could face charges - namely “aiding and abetting” - that are almost as serious as those likely to be levelled at the suspects. - Daily Mail