Feds Probe Boston Marathon Bombing Suspect's Link to Russian Militants

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.

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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.

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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.