Joshua Dratel, the attorney representing Katherine Russell, Tsarnaev's widow, said Russell's parents were questioned by the grand jury Thursday, though the nature of the questioning was kept secret.
Investigators haven't charged Russell, 25, or her parents in the April 15 twin bombings, which killed three people and injured 260 others, CNN reported.
Dzhokhar Tsarnaev, now 20, is suspected of carrying out the attacks with his brother Tamerlan, who was 26 when he died after being run over by his brother during a confrontation with police.
Dzhokhar is also accused of killing Massachusetts Institute of Technology police officer Sean Collier while trying to evade capture three days after the bombings.
Amat DeLuca, another lawyer representing Russell, said her client was "doing everything she can to assist with the investigation" eight days after the bombings. DeLuca said Russell knew nothing about the planned attack and was shocked to learn of her husband's involvement.