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Earlier in life, Boston Marathon terror suspect Tamerlan Tsarnaev boxed, dabbled in piano, and hung out at bars. But then, at some point four or five years ago, his interests dramatically shifted.
"It was about 2008, 2009 when these women say they saw Tamerlan begin to change," said NPR's Laura Sullivan, who spoke to former roommates of his wife, Katharine Russell. "He stopped drinking, he stopped smoking, and he, at that point, said to Katherine Russell that she also had to become a Muslim."
Tsarnaev was becoming increasingly strict in his Muslim beliefs. His uncle has accused a mysterious man - "Misha" - of brainwashing him, starting in 2009.
A U.S. government official tells CNN that the FBI has interviewed "Misha." We now know his full name is Mikhail Allack-Vierdov, and he lives in Rhode Island. Christian Caryl, of The New York Review of Books, tracked down "Misha," and he adamantly denied any involvement in Tsarnaev's radicalization.
"He was very, very, very intent on explaining that he had nothing to do with any kind of radicalization," said Caryl. "What he told me was, 'I was not his teacher. If I had been his teacher, I would have made sure that he knew that doing something like this was wrong.'"
Investigators are also looking into what role Tsarnaev's mother may have had in his radicalization. A U.S. official tells CNN that Russia intercepted a communication in 2011 between the suspects' mother, Zubeidat Tsarnaeva, and someone who may have been one of her sons "discussing jihad."
Sources also say she was added to the Terrorist Identities Datamart Environment, or TIDE, terrorism database at the same time as her son, after the Russians tipped off the U.S. in 2011. TIDE is a collection of more than half million names of suspected terrorists that is maintained by the National Counterterrorism Center.
"The older brother had been radicalized. He certainly had very strong radical tendencies. Probably his mother did as well," Rep. Peter King, R-New York, a member of the House Homeland Security Committee said.
Tamerlan Tsarnaev traveled to Russia in 2012. His time there, and whom he interacted with, are now the subject of intense scrutiny by investigators.
After he returned from Russia in July, Tsarnaev could no longer keep his extreme views to himself at the Boston mosque he attended. Mosque officials describe Tsarnaev as extreme and disruptive. Last November, after one preacher argued it was okay for Muslims to celebrate American holidays such as the Fourth of July, and Thanksgiving, alongside Muslim holidays, Tamerlan challenged the idea. In January of this year, when one preacher praised Martin Luther King, Jr., Tamerlan stood up and called the preacher a non-believer who contaminated people's minds.
"It was our community members who stood up and told him what he was doing is wrong," said Nichole Mossalam, executive director of the Islamic Society of Boston Mosque. "No words can describe how our community feels."
The internet is another factor in determining what led Tamerlan Tsarnaev down the path of extremism.
"It does look like a lot of the radicalization was self-radicalization online," said Rep. Adam Schiff, D-California, member of the House Intelligence Committee.
That seems to support what the surviving suspect, Dzhokhar Tsarnaev, has reportedly admitted. The preachings of radical cleric Anwar al-Awlaki were "likely" to have been among the videos they watched, according to a U.S. government official.
A source also tells CNN that one of the bombs found last week is similar to a design found in an online magazine run by an al Qaeda affiliate. Investigators are still sorting that out.
In many ways, the internet factor is the most troubling, because the material is still out there for anyone to see, and just a click away.