Female DNA was found on bomb components used in the attack this month on the Boston Marathon, a source familiar with the investigation confirmed to Fox News, though the source cautioned that it is too early to draw hard conclusions from that evidence.
"No one should expect that the investigation is over," the source told Fox News in confirming the development first reported by the Wall Street Journal, adding that it is just one piece of evidence that investigators are looking at.
The revelation about female DNA came on the same day that the FBI went inside the Rhode Island home of bomber Tamerlan Tsarnaev's widow's parents, and the nearby family of a man identified as his mysterious mentor hired a family spokesman to keep the media at bay.
"We are there as part of our ongoing investigation, but we aren't permitted to discuss specific aspects of our case," an FBI official said outside the suburban Providence home where Katherine Russell and her 3-year-old daughter are staying.
Authorities suspect Tsarnaev and his younger brother dropped, then detonated two bombs near the finish line of the April 15 marathon, killing three and injuring more than 260.
The 26-year-old Tamerlan Tsarnaev was killed several days after the bombing in a shootout with police. The 19-year-old brother, Dzhokhar Tsarnaev, was captured alive but wounded and is now at a medical detention center.
Russell has not been named as a suspect in the April 15 bombing. A home health aide, she reportedly worked up to 80 hours per week and did not know her radical Muslim husband's plans to carry out a terror plot. The widow has kept a low profile since the attack, and is believed to have been living with her parents in West Kingston, R.I., since her husband was exposed as a terrorist and then killed in a police shootout.
Meanwhile, an attorney for the family of a man who some of Tsarnaev's family members say is the mysterious "Misha" who radicalized Tamerlan Tsarnaev said his parents are under extreme stress and fearful of all the publicity the case has brought them. They confirmed their son, Mikhail Allakhrdov, is the Misha who was a spiritual tutor of Tsarnaev's some years ago. But in an interview with The New York Times, Allakhrdov, a Ukrainian Christian who converted to Islam, said he had not had contact with Tsarnaev for several years and that he never encouraged him to take up violence.
Richard Nicholson told reporters he expects law enforcement will "be asking additional questions" of the parents, implying that authorities have already spoken with the family.
"At some juncture they will be closing that part of the investigation," Nicholson said.
Fox News' Mike Levine contributed to this report.