Dratel said he has been told by prosecutors that Katherine Russell is not a target of the investigation.
Tamerlan's brother, Dzhokhar, was indicted on 30 counts in June and faces the possibility of the death penalty. Three of his friends were also indicted for allegedly lying to investigators or trying to cover up his role after the bombings.
Amato DeLuca, an attorney for Katherine Russell and her family, has said she didn't suspect her husband of anything before the bombings, and nothing seemed amiss in the days after. DeLuca told the AP on Thursday that her parents also knew nothing about their son-in-law's alleged involvement until after he was publicly identified by authorities.
There are many unanswered questions about what Russell knew or did before and after the bombings. The couple lived in the Tsarnaev family's cramped Cambridge apartment, where federal authorities have said the brothers assembled the bombs. Russell has never spoken publicly, although DeLuca has said she was working 70 to 80 hours per week as a home health aide and had no reason to suspect her husband of anything.
Dratel said the grand jury's investigation "is not necessarily an investigation of Katherine."
"It's an investigation of the entire situation," he said.
Russell, 24, grew up in an upper middle class family in the wooded suburban town of North Kingstown, Rhode Island, and met Tamerlan Tsarnaev when she was a student at Suffolk University in Boston. She had converted to Islam and was pregnant when they married at a Boston mosque in June 2010 against her family's wishes and advice, according to her grandmother. She gave birth to their daughter a few months later and dropped out of college.
Russell reverted to using her maiden name and moved with her daughter to her parents' Rhode Island home immediately after her husband was killed and brother-in-law was captured in a massive manhunt that shut down the Boston area.
Russell has never been charged with any wrongdoing, but she has been questioned several times and was followed for several weeks after the bombings by federal authorities. Federal officials ended surveillance of her home around the time her brother-in-law was indicted, according to neighbors.
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Smith reported from Providence, Rhode Island.