constructed.
The presence of genetic material does not necessarily mean a woman helped build the pressure-cooker bombs, said a law enforcement official, who spoke on condition of anonymity.
The genetic material could have come from a woman who was in the room where the devices were built, or from a cashier at a store where one of the bomb parts was purchased, the official said.
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.
Investigators are also casting a wider net for others who may have been associated with the alleged bombers, both in the US and in Russia, where the suspects' parents lived in the southern republic of Dagestan.
The Russian newspaper Novaya Gazeta quoted a Russian law enforcement source as saying that during a six-month visit to Dagestan in 2012, Tsarnaev was seen "more than once" meeting with Makhmud Mansur Nidal, suspected of being part of a rebel group that previously had planted two bombs in the Dagestani capital of Makhachkala.
Nidal, who was of joint Palestinian and Dagestani extraction, was killed May 19, 2012, when Russian authorities laid siege to a house where he and six other suspected insurgents were holed up, a Dagestani Interior Ministry official told the Los Angeles Times.
Novaya Gazeta reported that Russian agents also discovered that Tsarnaev had some online communications as early as 2010 with William Plotnikov, then 21, a Canadian citizen and Russian native who, like Tsarnaev, was a boxer. He had been living in the Toronto area with his family since 2005.
Plotnikov travelled to Dagestan purportedly to study Islam, but was one of eight people identified as insurgents killed by law enforcement forces on July 14, 2012, in one of Dagestan's remote mountain villages. Two days later, Tsarnaev left Dagestan for Moscow; a day after that, he left for the US, without waiting to receive the new passport that Russian officials have said was one of the purposes of his trip.
In the US, meantime, investigators appear to have questioned a man known as Misha previously named by Tamerlan Tsarnaev's family as one of those who influenced his increasingly strict adherence to Islamic teachings.
Mikhail Allakhverdov, a 39-year-old resident of Rhode Island, told the New York Review of Books that FBI officials had examined his computer and telephone as a result of his friendship with Tsarnaev.
He insisted he knew nothing about the bombings, and also said he had no role in teaching the Tsarnaevs.
