BOSTON (AP) — The in-laws of slain Boston Marathon bombing suspect Tamerlan Tsarnaev testified Thursday before a federal grand jury investigating the deadly April 15 attack.

Judith and Warren Russell, parents of Katherine Russell, declined to comment to The Associated Press as they entered the grand jury room in U.S. District Court in Boston.

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Katherine Russell is the widow of Tsarnaev, who was killed following a gunbattle with authorities pursuing him and his brother for allegedly setting off two bombs near the race’s finish line, killing three people and wounding more than 260.

The U.S. Attorney’s office would not comment on whether Russell or anyone else is being investigated or why a grand jury continues to meet after four people have already been indicted.

Josh Dratel, a lawyer who represents Katherine Russell and her family, said her parents appeared after being subpoenaed to testify, and said they “told the truth.”

Dratel said he has been told by prosecutors that Katherine Russell is not a target of the investigation. When asked if he is concerned she could eventually become a target, Dratel said that could only result from political, not legal, motivations.

“We don’t have concern that a professional prosecutor is going to look at it and see it as a basis for charging (Katherine),” Dratel said.

Dratel noted the high-profile nature of the terrorism case and the media frenzy that has accompanied it.

“We know that there’s been pressure on law enforcement and the Justice Department in this case. We don’t want her to be scapegoated as a result of that pressure.”

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.

“They don’t know anything. They have no knowledge,” he said. When asked why they were called appear before the grand jury, DeLuca said, “They met Tamerlan, so I’m sure they’re being asked about his background.”

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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, R.I., 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.

David Zlotnick, a professor at Roger Williams University School of Law and a former federal prosecutor, said the only reasons to keep a grand jury investigation going are if prosecutors believe there are still people who might need to be charged or that there could be additional charges for those already under indictment.

“I’m amazed this is still going on. One bomber’s dead. The other one they have lock-solid proof of his guilt,” he said.

Zlotnick said momentum might be the cause of the continuing investigation.

“Once the federal law enforcement system gears up and devotes resources, sometimes it has a life of its own. When do you stop?” he said. “They were told, get to the bottom of this, at some point someone has to take the politically unpopular step of ending it.”

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