She was known as Katie, a pretty, popular girl from a well-respected Rhode Island family. In high school, she excelled at music and art and worshipped David Bowie. As a freshman at Suffolk University, she majored in communications, and she and a gaggle of friends modeled themselves after the girls on “Sex and the City.”

She thought about joining the Peace Corps.

That was before 2010, when she met the man she’d drop out of school to marry, the man for whom she’d convert to Islam, the man who, three years later, would leave her with a baby daughter and the threat of jail time.

Today, at 25, Katie Russell is best known as the widow of the Boston bomber. As the first anniversary of the attack nears, she remains one of its biggest mysteries — how she was drawn into her husband’s world, and what she knew about his plans.

In November, Russell’s brother-in-law, Dzhokhar “Jahar” Tsarnaev, will stand trial. Russell has not been charged, nor is it clear whether she’ll be a witness. But authorities still wonder: Was she a willing accomplice? Or a witless victim?

Russell, the oldest of three girls, was raised on a tree-lined street in the comfortable suburb of North Kingston, RI, right off a bike path called Sage Trail. Her dad, Warren, is an emergency-room doctor, her mom, Judith, a nurse.

The girls were raised Catholic and went to public schools. Katie was most comfortable in jeans and T-shirts. “She was a great girl, and a good student, and normal,” a family friend told The Washington Post. “She was normal.”

Aside from one incident when she was 18 — she was arrested for shoplifting $67 worth of merchandise at an Old Navy — Russell was never in trouble. (The charges were dropped after she did community service and paid a $200 fine.) Her personal credo, according to high-school friends, was, “Do something about it or stop complaining about it.”

“It was a fairly tight-knit family,” said the family friend, adding that the girls “had plenty of freedom . . . not like some kids where it’s not allowed for boys to see girls or girls to see boys.”

One night in 2009, two years ­after enrolling at Suffolk University in Boston, she met a charismatic young boxer named Tamerlan Tsarnaev in a nightclub. At the time, he had a girlfriend: 19-year-old Nadine Ascencao, whom he had been dating for three years.

But Tsarnaev, who emigrated with his refugee family from a former Soviet republic in 1995, had undergone a sudden religious conversion. In 2008, he went from smoking pot, partying and dressing “like a pimp, kind of ­Eurotrash,” a neighbor said, to hanging out at the local mosque.

“One minute, he’s this funny, normal guy who liked boxing and having fun, the next he’s praying four times a day, watching Islamic videos and talking insane nonsense,” Ascencao told Britain’s Sun tabloid. “Tamerlan said I couldn’t be with him unless I became a Muslim. He wanted me to hate America like he did.”

He became controlling and abusive, telling Ascencao she was no longer allowed to listen to the ­radio or watch TV. She’d lost her virginity to him, but now, he said, they had to stop having sex. As long as they were unmarried, it was against Muslim law. He told her she had to drop all of her old friends and socialize only with Muslim girls.

“He once ripped a pair of my jeans and hit me in the face with them,” she said. Another time, he slammed her head into a car after she wore shorts and a tank to a party. She called 911 but declined to press charges.

Toward the end of their relationship, when Ascencao finally relented and wore a hijab, he’d taunt her about the other American girl he had been seeing, the one who took Islam far more seriously than she did.

“He once made me learn a verse of an Islamic prayer,” she recalled. “And if I got it wrong, he’d say, ‘Well, Katherine can do it.’ ”

In 2009, Tsarnaev dumped ­Ascencao and began seriously seeing Russell. Russell began pulling away from her family and friends. Her parents were suspicious of Tsarnaev, mainly because he had no job and no plans to get one. He told everyone he was going to be an Olympian.

A close family friend told The Washington Post he attempted to intervene and invited Russell to dinner. He was too late. Russell declared that she was becoming a Muslim and that he’d soon be seeing her in a head scarf.

“The psychology of it isn’t ­understood by any of us,” he said. But “Katie didn’t care.”

She was, friends said, infatuated, seemingly oblivious to the stares she was drawing on campus. Russell’s college roommate was convinced it was an abusive relationship.

“She stopped drinking and wouldn’t come around as much and kind of judged us for wanting to go out, and he would forbid her for wanting to go out with us,” she told CBS News. “He became very violent with her and was brainwashing her into converting into Muslim.”

Other roommates told NPR that Tsarnaev called her “slut” and “a prostitute” and threw pieces of furniture at her. Despite his supposed piety, Tsarnaev and Russell had premarital sex at least once. By early 2010, she was pregnant with their daughter, Zahara.

By that spring, Russell was living near Tsarnaev — who still resided with his family — in Cambridge, Mass. They married six months after they met, on June 21, 2010, on the third floor of a ramshackle mosque in Dorchester. There were no guests, just two witnesses, and the ceremony lasted 15 minutes. The imam who married the couple had never met them before and never saw them again.

Russell changed her name. Now she was Karima Tsarnaeva. She dropped out of school and moved into the cramped Tsarnaev family apartment. The whole family, including Tsarnaev’s younger brother, Dzhokhar, and two sisters lived there. His parents were on and off welfare, and the rent was subsidized by a Section 8 voucher.

The whole Tsarnaev family was loathed by the neighborhood. They were loud, obnoxious, entitled, the father dumping his waste into other people’s garbage cans and taking up parking spaces with the beat-up cars he tinkered with. Their landlord begged them to move out. Every month, they’d haggle over rent.

None of them, except Russell, had a job. “He wasn’t really willing to work,” a family friend of Russell told The Washington Post. “That, in my mind, made him an unsuitable husband. She worked like crazy for him.”

According to one of her attorneys, Russell put in 80-hour weeks as a home health-care aide. Still, she and Tsarnaev found themselves on food stamps, too.

“He was a douche bag,” her friend Jesse Coyle told People magazine. “Her friends didn’t like him. He made her get rid of her Facebook account, and she ­always had to text him and let him know what she was doing.”

It was unclear what her husband did all day while she was at work, but Russell knew not to ask. In his presence, she shrunk and went silent. “He’s a very strong personality,” a clerk at their grocer told The Washington Post. He added that Tsarnaev would boss her around, that only he would choose the food and pay for it, that she would make no eye contact and say nothing.

“Maybe she loved him a lot,” the grocer said. “But it seemed odd. She’s a woman living in America. This is America.”

Where Russell was on April 15, 2013 — the day of the Boston Marathon bombings — is still unknown. According to a report in The Associated Press, her lawyer, Amato DeLuca, said that the last time she saw her husband was early in the morning as she left their apartment for work on April 18.

It was the last day of Tsarnaev’s life. He and Dzhokhar had been identified by the FBI, then the media, as the bombers. They were now the targets of a nationwide manhunt.

They went on the run, killing a cop on the MIT campus and carjacking a Mercedes SUV before a Watertown officer spotted them a little after 1 a.m. A wild gunfight ensued, and while Tamerlan sustained gunshot wounds to his torso and extremities, he was killed when his brother, making his escape, ran over him with the SUV. Dzhokhar was later captured alive.

Russell has always claimed to be shocked and appalled by her husband’s actions, and to have had no knowledge whatsoever of what he was planning. She has also maintained that she never helped him try to escape, and when police reported that Tamerlan was also a suspect in a grisly triple murder in Waltham, Mass., that took place on Sept. 11, 2011, she claimed ignorance, too.

One source in the investigation told People that one theory has Russell as not so much a co-conspirator but an abused, unknowing enabler. “The big question is, what did she either wittingly or unwittingly do to help her husband?” the source asked.

Phone records show that Russell spoke to Tsarnaev on April 18, and another law-enforcement source told The Weekly Standard that after seeing the brothers identified on television, she called her husband.

“She notified him,” said the source, “and there certainly didn’t seem to be any notion of surprise — just a report that ‘you’re being watched.’ ”

Following her husband’s death, Russell fled to her parents’ home back in North Kingston, and the FBI descended on the tiny apartment in Cambridge. There they found bomb-making residue in the kitchen sink, in the bathtub, and on the kitchen table.

On Russell’s laptop, they found the first issue of the al Qaeda online magazine Inspire, which included an article titled “How to Make a Bomb in the Kitchen of Your Mom.”

Russell said nothing. Through her lawyer, though, she made it known that she would not be claiming her husband’s body. Her parents tacked a self-pitying note on their front door, pleading with the press for mercy.

“Our daughter lost her husband today, the father of her child,” it read. “Please respect our family’s privacy in this difficult time.”

When the FBI showed up at her parents’ home on April 21, 2013, Russell refused to speak with them, and when it was reported, on May 3, that no trace of her DNA was found on any of the explosive material, she made it clear she would not cooperate.

Authorities have yet to bring charges, but have made it clear that spousal privilege — which holds that one spouse cannot be compelled to testify against the other — no longer applies when one of them has died.

It remains unclear whether Russell will face a grand jury, or be called to testify. In the meantime, she has allowed family, friends and her lawyer to tell the world how she is reverting to the normal, all-American girl she once was. She was now going to movies, listening to rock ’n’ roll, wearing nail polish, eating at fast-food joints and drinking coffee at Starbucks — all the things forbidden in her life with Tamerlan.

She took back her maiden name and hired New York City-based lawyer Joshua Dratel, who has represented dozens of high-profile terrorists. (Dratel declined comment for this article.)

As recently as four months ­after the bombings, “we’re seeing glimpses of the old Katie again, and it’s wonderful,” a relative told People. But not everything has changed.

“She has made it clear to her entire family that she is a Muslim and will remain a Muslim. That’s non-negotiable.”