April 30, 2013  -- Accused Boston Marathon bomber Tamerlan Tsarnaev may have been in touch with suspected militants before and during his visit last year to southern Russia, according to a U.S. official and sources in the region.

American officials are investigating whether Tsarnaev had been in contact over the internet with a man named William Plotnikov, a Russian-Canadian and a fellow boxer, who had converted to Islam and joined the militant insurgency in the North Caucasus. Authorities also want to know what Tsarnaev was doing with a known militant recruiter in the region named Mansur Mukhamed Nidal with whom Tsarnaev was repeatedly seen leaving a controversial mosque in Makhachkala, the capital of Dagestan.

The new leads come as the FBI's investigation into the deadly April 15 bombing at the Boston Marathon continues to expand and follows the discovery of female DNA on one of the bombs, according to government sources. The sources said it is unclear whether the DNA was from a victim of the attack, from someone who handled components of the bomb before it was assembled or from a possible co-conspirator of the suspected Tsarnaev brothers.

READ: Boston Bombing Suspect Charged With Using Weapon of Mass Destruction

In addition to identifying the woman in question, people briefed on the case said the FBI reportedly is now seeking information on almost a dozen persons of interest.

"Some may have been involved in helping build the bombs. Others may have been involved in helping radicalize the brothers," Seth Jones, counter-terrorism expert at the RAND Corporation, said on "Good Morning America" today.

Officials said Monday the FBI is seeking DNA samples from Tamerlan's wife, Katherine Russell, and investigators were seen leaving her home with a set of evidence bags.

Three people were killed and more than 260 others were injured when a pair of bombs ripped through the crowd near the finish line at the Boston Marathon earlier this month. After investigators identified Tamerlan and Dzhokhar Tsarnaev as suspects based on surveillance footage from the event, Tamerlan was killed in a shootout with police and Dzhokhar was injured and later captured.

As he recovered from his injuries, Dzhokhar reportedly told investigators the deadly plot had been hatched using the internet as a guide and said he and his brother were not directed or funded by any foreign government or rogue group. He has since stopped cooperating with investigators, officials said.

READ: Feds Make Miranda Rights Exception for Marathon Bombing Suspect

Still, U.S. officials are closely reviewing Tamerlan's 2012 visit to Dagestan, which his parents said he undertook ostensibly to visit family and to pick up a Russian passport. A family member told ABC News earlier this month that during his stay in Russia, Tamerlan was kicked out of the house after expressing his increasingly extremist views on religion.

Then, in July, he vanished, leaving that new passport behind and left Russia to return to the U.S. His sudden departure is now raising eyebrows as it came after a flurry of police raids in Russia that left both Plotnikov and Nidal dead.

According to a source in Dagestan, Tsarnaev and Plotnikov are believed to have communicated via VKontake, a Russian social networking website similar to Facebook. The source said after Plotnikov was killed on July 13, Tsarnaev removed him and others from his contact list on the site.

Tsarnaev's parents have denied their son was involved with any militant or extremist groups, insisting Tamerlan and Dzhokhar are being framed by the U.S. government.

In late 2011, the CIA requested that Tamerlan Tsarnaev and his mother be placed in a U.S. terrorism database after it received information from the Russian government that the pair could be potential Islamic militants. By that time the FBI had already looked into Tamerlan and determined he did not have ties to terrorism. U.S. officials recently learned that Russian forces had wiretapped conversations between Tamerlan and his mother.

America's Director of National Intelligence, James Clapper, has called for an intelligence community review of how information on Tamerlan was handled prior to the Boston attack – a move President Obama said today was "standard procedure around here."

"We want to leave no stone unturned," Obama said.

Overnight new video emerged from a boxing documentary that featured Tamerlan Tsarnaev from his days as a fighter trying to make the U.S. Olympic team.

In a short clip of the 2010 video, obtained by Entertainment Tonight, Tamerlan is seen wearing his boxing gear and says his name while smiling broadly for the camera.

ABC News' Megan Chuchmach and Luis Martinez contributed to this report.

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