FBI special agents spent about 90 minutes Monday inside the Rhode Island home of the parents of Katherine Russell, the widow of suspected Boston Marathon bomber Tamerlan Tsarnaev, an FBI spokesman said.

Special Agent Jason Pack said the agents visited the North Kingstown house as part of their investigation of the bombing. Russell has been staying at her parents’ home.

“The FBI is there as part of our ongoing investigation, but we aren’t permitted to discuss specific aspects our case,” Pack said.

Russell has not spoken publicly and said nothing to reporters when she left the home shortly after the agents departed. Her attorney said last week that Russell had no involvement in the bombing that killed three and injured more than 250 during the marathon on April 15.

“She is doing everything she can to assist with the investigation,” Amato DeLuca, Russell’s attorney, said in a statement . “The report of involvement by her husband and brother-in-law came as an absolute shock to them all.”

A chronology of the Tsarnaev family.

Two law enforcement officials said that investigators found female DNA on a piece of one of the bombs from the marathon. The DNA could have come from a woman who helped the suspects make the bombs or from a person in a store who handled the materials the suspects bought, said the officials, who spoke on the condition of anonymity to discuss the ongoing investigation. The DNA may have also come from someone in the crowd of people at the marathon, one of the officials said.

Tamerlan Tsarnaev, 26, was killed in a shootout with the police four days after the bombing. His brother, Dzhokhar, 19, is recovering from gunshot wounds and he has been charged with using a weapon of mass destruction.

Judith Clarke, a defense lawyer, was appointed by a magistrate Monday to represent Dzhokhar. She has represented high-profile defendants, including Unabomber Ted Kaczynski and Jared Loughner, who wounded Rep. Gabrielle Giffords and killed six people in Tucson.

The FBI has interviewed Mikhail Allakhverdov, known as “Misha,” after relatives of Tamerlan Tsarnaev said that someone named Misha was responsible for radicalizing Tsarnaev.

Allakhverdov, who also lives in Rhode Island, told the New York Review of Books that he was a convert to Islam and he had known Tsarnaev. But he said he was not Tsarnaev’s teacher and denied any part in the bombings. He also said he is cooperating with the FBI investigation.

Attempts to reach Allakhverdov by phone were unsuccessful, but a lawyer for his family told reporters that he expects the inquiry to be closed soon.