The FBI has found female DNA on at least one of the two homemade bombs detonated during the Boston Marathon.
The presence of genetic material does not necessarily mean a woman helped build the pressure-cooker bombs, said a law enforcement official.
The DNA could have come from a woman who was in the room where the bomb was being built, or she might have sold it to brothers Tamerlan and Dzhokhar Tsarnaev.
The test results have prompted investigators to look more closely at women who may have had contact with the alleged bombers, Tamerlan Tsarnaev and his younger brother, Dzhokhar Tsarnaev.
Investigators are collecting DNA samples from some women who were close to the pair to provide a comparison.
On Monday, investigators visited the Rhode Island home of the family of Katherine Russell, the widow of the elder brother, who was killed in a shoot-out with police on April 19.
Dzhokhar Tsarnaev was wounded but captured, and faces federal charges of using a weapon of mass destruction.
The two remote-controlled bombs killed three people and injured more than 260 at the marathon on April 15.
Photo: Media wait outside home of Warren and Judith Russell, where their daughter Katherine, widow of Tamerlan Tsarnaev, is staying (Getty Images)