Did Boston bombers have help? Investigators checking female DNA evidence.

Boston bombing investigators reportedly have found female DNA evidence on one of the pressure cookers used in the attack, but there could be a number of explanations for that.

Michael Dwyer/AP
Pedestrians pass the spot where the first bomb detonated on Boylston Street near the finish line of the Boston Marathon, in Boston, last week.

Investigators have found female DNA on a piece of one of the pressure cookers used as bombs in the Boston Marathon attacks, but it’s unclear whether the new evidence points to a third suspect, officials briefed on the probe told The Wall Street Journal.

The DNA does not conclusively indicate that the bombing suspects – brothers Tamerlan and Dzhokhar Tsarnaev – had an accomplice who helped to either build the bombs or dispose of the evidence. Officials said that the DNA could have come from a store clerk who handled the materials, or from a spectator at the bombing site.

But investigators are using the DNA evidence, as well as a fingerprint found on a bomb fragment, to identify several potential associates, including Katherine Russell, the widow of deceased suspect Tamerlan Tsarnaev, two senior law enforcement officials told The New York Times.

FBI agents visited Ms. Russell at her parents’ home in North Kingstown, R.I., on Monday. They left the house carrying bags labeled “DNA samples,” which will be used to see if the DNA belongs to Russell or the couple’s 3-year-old daughter, officials told CNN. Russell has been staying with her parents since April 19, when Tamerlan Tsarnaev died after a shootout with police.

"The FBI is there as part of our ongoing investigation, but we aren't permitted to discuss specific aspects of the case," FBI spokesman Jason Pack told the Journal.

Russell has not been charged in the plot, and investigators say she is not currently a suspect. Her lawyer, Amato A. DeLuca, has said that his client was shocked to learn of her husband’s alleged involvement in the attacks, and she has been cooperating with the investigation.

“We want to state what we stated before: Katie continues to assist in the investigation in any way that she can,” he said in an e-mail to The New York Times on Monday.

Police found materials used to make the bomb in the apartment where Russell and her husband lived in Cambridge, Mass., Reuters reported. But Mr. DeLuca said Russell did not know about her husband’s activities because she worked when Mr. Tsarnaev was at home watching their daughter.

Even if the female DNA turns out to be Russell’s, it is not proof that she participated in building the bomb or plotting the attack, experts say.

“It certainly becomes a circumstantial piece that says she may have handled the device or parts of the device and that opens the door she may have known,” said John Miller, a former assistant FBI director, Tuesday on “CBS This Morning.”

"What they found in the apartment was black powder and parts, but not the workbench you would need to have to make these bombs. They are still looking for that, another place,” Mr. Miller said.

A law enforcement official told the Times that the FBI does not believe that the Tsarnaev brothers were connected with a terrorist network, but there is skepticism about whether other people knew about their plans or helped them destroy evidence. There is no hard evidence to support that theory, but it’s possible that people close to the Tsarnaevs may have unknowingly disposed of evidence, officials told the Journal.

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