The FBI has found female DNA on one of the pressure cookers used in the Boston Marathon bombings.

Katherine Russell (WLNE TV)

It has not been identified, reports the Wall Street Journal, and could also belong to one of the bombing victims.

The report comes after FBI agents investigating the Boston Marathon bombings  visited the Rhode Island home of dead suspect Tamerlan Tsarnaev's  in-laws and carried away several bags.

CNN says at least one bag was labeled DNA samples.

FBI spokesman Jason Pack confirms agents went to the North Kingstown home of Katherine Russell's parents Monday. Russell is Tsarnaev's widow and has been staying there.

Russell gave a DNA sample to investigators according to the Wall Street Journal, which reports that the FBI had been negotiating with her attorney to question her. She has been too distraught over her husband's death to speak at length with agents.

Attorney Amato DeLuca says she's doing everything she can to assist with the investigation.

Attorneys have said Russell and her family were in shock when they learned of the allegations against her husband and brother-in-law, Dzhokhar Tsarnaev.

The FBI is also looking into the connection between  Tamerlan Tsarnaev and William Plotnikov, a boxer who moved with his parents from Russia to Canada before joining militants in the North Caucasus according to the Journal report.

Tamerlan Tsarnaev was killed in a gunbattle with police. Dzhokhar Tsarnaev has been charged with using a weapon of mass destruction. Their mother calls the allegations lies.