MOSCOW -- In a few months, starting last August, the YouTube account in the name of Tamerlan Tsarnaev took on an increasingly puritanical religious tone. It moved from secular militancy to Islamist certainty.
It seemed to mirror the wars in the Caucasus, which shifted from a separatist conflict in Chechnya in the 1990s to a jihadist campaign that continues to this day in neighboring Dagestan.
Tsarnaev, a 26-year-old ethnic Chechen believed to have been one of the Boston Marathon bombers, died after a shootout with police in Watertown, Mass., on Thursday night. His younger brother Dzhokhar, arrested and hospitalized Friday night, is the only other suspect.
The exact trajectory of Tsarnaev's journey into radicalism is still emerging, but it first surfaced in 2011 when he somehow entered the radar of the Russian security services. It accelerated in late 2012 upon his return to the United States from a six-month visit to the Caucasus, when friends and relatives noticed a new religious and political fervor. And it ended in violent death after he was identified by the FBI as one of the suspects in a coordinated bombing that killed three and injured more than 170 near the finish line of Monday's race.
The motivation of Dzhokhar Tsarnaev, 19, is less clear, and federal agents have not interrogated him in any depth because he is recovering from gunshot wounds.
"The influence of the older brother could have been critical," said Bruce Hoffman, a professor of security studies at Georgetown University. He said the possible role of the older man reminded him of 2007 bombings in London, in which a cell leader radicalized the youngest member of the group. In that case, the teenage bomber "was much more impressionable and much more a follower."
A Russian security agency asked the FBI for information on Tsarnaev in early 2011, almost certainly because of communications with individuals in Russia or other activity on the Internet that brought him to their attention.
The FBI, in a statement released Friday night, said it scrutinized Tsarnaev and visited him and his family in 2011, but found no grounds for further action. After two months, the file on Tsarnaev was closed, according to a U.S. law enforcement official.
The Russian request had mentioned a concern that Tsarnaev was headed to a "region" in his homeland -- most likely Dagestan -- to join an underground group. The American agency said it asked its Russian counterpart for more information, but it received no response.
Although the United States and Russia have some limited exchange of information on counterterrorism matters, there is little real cooperation, and the security relationship has been damaged by broader diplomatic tensions between the two countries.
"My sense is that the cooperation is not very good," said Thomas Hegghammer, a senior research fellow at the Norwegian Defence Research Establishment in Oslo. "And that may be why in this particular case the Russian information was taken with a pinch of salt."
Russian security agencies have little interest in actual cooperation or joint operations, said Andrei Soldatov, co-author of the book "The New Nobility: The Restoration of Russia's Security State and the Enduring Legacy of the KGB" - despite a Kremlin announcement Saturday that President Barack Obama and President Vladimir Putin had agreed to step up combined anti-terror efforts.
The conflict in the Caucasus, long regarded as a largely Russian problem, has begun to draw more attention from Western intelligence agencies, with the arrest of suspected terrorists from the region in Western Europe. Last August, two Chechens and a Turk were arrested in Spain and accused of planning attacks on a shopping center in Gibraltar and a joint U.S.-Spanish naval base in Rota, Spain. For several years prior to 2011, one of the Chechens operated between Dagestan and the tribal areas of Pakistan, according to Spanish officials. In February, three more Chechens who are believed to be part of the same cell were arrested in France.
Tamerlan Tsarnaev left for Russia in January 2012, and spent half the year there. In interviews Friday night, his father said he had stayed with him in the regional capital of Makhachkala -- far from the rural centers of the radicals -- rising at noon and spending his waking hours among members of his extended family.
Even if Tsarnaev's long trip away from his wife and baby was entirely benign, the oppressive, fearful atmosphere blanketing the Russian republic was unavoidable. Tsarnaev arrived in Dagestan at a bloody time. Suicide bombing, then and later, has long been a favored method of assassination, in contrast to the bombs used in Boston.
A police operation in Dagestan and Chechnya in mid-February last year, shortly after Tsarnaev's arrival in the region, led to the deaths of 17 police officers. Twenty-four others were wounded. On March 7, 2012, a female suicide bomber killed herself and five police officers. Less than two weeks later, on March 23, a Muslim cleric and his bodyguard were killed by a remote-controlled bomb. Ten days later, three rebels and a soldier died in a gun battle.
And on May 4 in Makhachkala, where Tsarnaev was staying, two suicide car bombs killed 13 people and wounded more than 100.
In July, Russian security officials announced that for the first six months of the year, through all of the North Caucasus, 194 militants had been killed, along with 104 police officers and 32 civilians. They expressed satisfaction that this represented a decline from the year before.
After returning from Dagestan, Tsarnaev appeared to be constructing his own religion-based ideology, moving between often contradictory ideas as he explored different websites. That's not so surprising, Grigory Shvedov, chief editor of a news service called Caucasian Knot, said Saturday. Young Muslims from the former Soviet Union often have only the haziest notion of their religious and cultural heritage, following 70 years of communism in the region for most of the 20th century.
Among Tsarnaev's earliest YouTube postings, which include a selection of secular dance mixes, is a video of Timur Mutsuraev, the bard of Chechen separatism. After two devastating wars of secession, between 1994 and 2003, Chechnya remains within the Russian Federation, under the thumb of the strongman Ramzan Kadyrov.
Today Chechnya is exceptionally quiet, but the conflict has spilled over into neighboring Dagestan and become a struggle with an often-radical religious complexion. There, imams, militants and police are killed every week, while fundamentalists struggle against traditional Sufi religious leaders. One aspect of the conflict is the corruption and plundering that accompany it, primarily by government forces, Nadira Isaeva, a journalist who was forced to flee Dagestan at the time Tsarnaev arrived there, wrote in an e-mail from the United States.
Starting a playlist as soon as he returned to Boston, with an independence song by Mutsuraev, suggests that Tsarnaev could have been thinking about his ethnic roots and perhaps a recently stoked antagonism toward Russia. Although the singer is now quite moderate, his earlier songs are unequivocal. "He is the most influential poet, and singer, on the Chechen war," Shvedov said. "He is a guy who still motivates a lot of people to fight."
But as the playlist developed, videos of the puritanical Sheikh Feiz Muhammad, an Australian, appeared. He is someone for whom Mutsuraev, as a musician, would be anathema, yet they are listed almost one after the other on the playlist. The videos of Feiz Muhammad promote a radical cleric who, in 2010, called on Muslims to behead the Dutch politician Geert Wilders, according to the Dutch newspaper De Telegraaf.
Tsarnaev's private pursuits began to manifest themselves publicly. His aunt, Maret Tsarnaeva, told reporters at a Toronto news conference that her nephew, who previously seemed to have little interest in religion, had recently begun to pray five times a day. He grew a beard and was vocal about religion and politics.
Albrecht Ammon, 21, who has an apartment on the second floor of the house on Norfolk Street in Cambridge, Mass. where Tsarnaev lived, said he recently had an argument in a pizza parlor with Tsarnaev about the Bible and American foreign policy.
Ammon said Tsarnaev expressed the view that "the Bible is a cheap copy of the Koran" and that the United States goes to war based on the Bible. He also said that "in Afghanistan, most casualties are innocent bystanders killed by American soldiers," according to Ammon, who is a senior at Cambridge Rindge and Latin School, which Dzhokhar Tsarnaev attended.
"It seemed like he didn't have something against the American people," recalled Ammon, "he had something against the American government, which baffles me with the marathon."