LATEST! After female DNA is found on Boston bomb fragment, law enforcement wants to know: What is bomber widow KATHERINE RUSSELL TAMERLAN hiding?!

The American wife of sus­pected Boston Marathon bomber Tamerlan Tsar­naev fell completely under his spell, sources say – and now sources believe he may have duped her into hiding his role in the bloody attack!

While the FBI continues to probe what Katherine Russell Tsarnaev knew about the bombing, The ENQUIRER has uncovered a secret arrest in the 24-year-old widow’s past that may be linked to her evil bomb-planting husband.

“Tamerlan had an iron-clad grip on Katherine,” a friend in her native Rhode Island told The ENQUIRER.

“He turned her from an innocent all-American girl into a terrorist bride. It was like he brainwashed her! She must have known something about his activities before the marathon, and now she may unwittingly be hid­ing information that’s vital to national security – after all they have a 2-year-old child!”

 While Katherine’s at­torney Amato DeLuca insists she knew nothing about the bomb plot, the FBI scoured video of the marathon and showed her picture to witnesses, accord­ing to reports.

Meanwhile, The EN­QUIRER has conducted an exhaustive investigation of Katherine’s background, and discovered that while she reportedly met Tsar­naev as a Suffolk University student in Boston, she was already claiming to be mar­ried in 2007!

THE ENQUIRER also learned Tamerlan dragged Katherine into an ugly love triangle that ended with a violent domestic assault. According to court documents, police responded to a domestic incident at Tamerlan’s res­idence in Cambridge, Mass., on July 28, 2009. The victim, identified as 22-year-old Nadine Ascencao, “called 911 on her cell phone, indicating she was beat up by her boyfriend…and was crying hysterically,” according to the document.

Ascencao told police that she was yelling at her boyfriend – identified as Tamerlan Tsarnaev – “because of another girl.” Reports say it was Russell. When officers asked Tsarnaev if he’d hit Ascencao, “he stated, ‘Yes, I slapped her,’” the report said.

Tsarnaev was arrested for assault and battery, but records show the charges were later dismissed for lack of prosecution.

As The ENQUIRER reported previously Katherine has a secret arrest record. EXCLUSIVE COVER STORY: BOSTON TERROR WIFE’s SECRET ARREST

Katherine reportedly converted to Islam for Tsarnaev, and had been working 70 to 80 hours a week as a home health aide while he cared for their daughter Zahara, 2

“Now that Tamerlan is dead, I hope that Katherine will tell authorities ev­erything she knows about him and his brother,” said the source. “For her family’s sake, I pray that she didn’t have any direct knowledge of the bombing.”

Yesterday, April 29th, FBI agents Monday visited the Rhode Island family home of Katherine Russell . She’s staying with her parents – dad Warren, 55, an emergency room physician, and mom Judith, 56, a nurse – in their colonial-style, two-story $400,000 Rhode Island home.

Agents were there to collect a DNA sample from Russell to compare it against the female DNA found on a bomb fragment at the blast scene.

 Investigators say a lab test could help them determine if Russell ever had contact with the device.

Law enforcement say Russell is not a suspect and has not been charged in the terror plot.