To her neighbors, Katherine Russell was living like a ghost, rarely seen and never heard after her husband and brother-in-law were accused of plotting together and planting bombs that killed three people and injured more than 260 near the marathon's finish line.

Federal investigators have questioned Russell, who married Tamerlan Tsarnaev in 2010, but they haven't revealed what she told them.

It's one of many questions looming as the trial for Dzhokhar Tsarnaev, her brother-in-law, starts this week.

Federal prosecutors will not say if Russell, 25, is a suspect, a witness or simply a noninvolved widow. There have been no charges filed against her.

Here are five things we know about Russell.

1. She has said she was in the dark about the Tsaranaev brothers' alleged plans.

Investigators believe the pressure cooker bombs that went off at the marathon were at least partially made on the kitchen table of the tiny apartment she shared with Tamerlan Tsarnaev.

The last time Russell saw her husband alive was just hours before he died in a gunbattle with police, a source close to the family told CNN shortly after the bombings.

Her attorney told CNN that she learned through news reports that her husband and brother-in-law were suspects in the attacks. It was devastating news for the whole family, he said.

"The reports of involvement by her husband and brother-in-law came as an absolute shock to them all," attorney Amato DeLuca said in a 2013 statement. "As a mother, a sister, a daughter, a wife, Katie deeply mourns the pain and loss to innocent victims -- students, law enforcement, families and our community. In the aftermath of this tragedy, she, her daughter and her family are trying to come to terms with these events."

2. She was arrested for theft.

Before the bombings, Russell had one run-in with the law. In June 2007, she was arrested for stealing $67 in goods from Old Navy.

According to court records, she acknowledged the theft and gave back the merchandise.

Last year, she appeared in court over a traffic ticket.

3. Her last known address was near her in-laws.

By all indications, Russell has chosen to be near -- and with -- her dead husband's family living in New Jersey, rather than with her parents in Rhode Island.

Her last known apartment was just blocks from the last listed address of Ailina and Bella Tsarnaeva, her sisters-in-law.

And she was last seen holding the newest child in the Tsarnaev family, her niece.

Ailina Tsarnaeva recently appeared in court on unrelated charges of threatening a romantic rival with a bomb. She has pleaded not guilty.

4. Russell was raised Christian.

She converted to Islam before she married Tsarnaev at a Massachusetts mosque in June 2010.

5. She and Tamerlan Tsarnaev had one child together.

Their daughter was a toddler at the time of the bombings. The last time Russell saw her husband alive, the family source said, she was handing off their daughter to stay with him while she went to work as a home health aide.

(CNN)