The FBI has removed evidence including DNA samples from the house where the widow of suspected Boston Marathon bomber Tamerlan Tsarnaev is now living.
Katherine Russell, 24, has been staying at her parents' house in Rhode Island since her husband's death.
US media report that investigators are analysing female DNA found on a piece of the pressure-cooker bombs used in the attacks.
Three people were killed and more than 260 injured in the blasts at 2.50pm on 15 April near the finish line of the marathon.
The New York Times reports officers also took a sample of Ms Russell's DNA.
Tamerlan Tsarnaev was killed in a gun battle with police on the night of Thursday, 18 April. His younger brother Dzhokhar, 19, is under arrest. He is charged with using a weapon of mass destruction.
Ms Russell's lawyer said she was doing everything she could to assist with the investigation. She has lived at her parents' house since Tamerlan Tsarnaev was killed.
The BBC reports the couple lived with their young daughter in an apartment in Cambridge, Massachusetts. Police say they have found bomb material at the residence.
Ms Russell's lawyers say she did not know much about her husband's activities because she spent most of her time outside the home working as a health aide while he watched their child.