WASHINGTON — Tamerlan and Dzhokhar Tsarnaev sought to embrace American lives after emigrating from Russia – joining a boxing club, winning a scholarship and even seeking U.S. citizenship. But their uncle last week angrily called them “losers” who failed to feel settled even after a decade of living in the United States.

The disparity between the brothers’ struggle to assimilate in the U.S. and their alleged bombing of the Boston Marathon reflects what counterterror experts describe as a classic pattern of young first- or second-generation immigrants striking out after struggling to fit in. The U.S. has long been worried about people in America who are not tied to any designated terrorist group but who are motivated by ideologies that lead them to commit violent acts. Some are motivated by radical religious interpretations; others feel ostracized by their communities.

Three U.S. officials involved in the investigation said the brothers had no links to any terrorist groups. After interrogating Dzhokhar Tsarnaev on Monday, U.S. officials have concluded, based on a preliminary interrogation and other evidence, that they were motivated by their faith, apparently an anti-American, radical version of Islam. Another official called them aspiring jihadists. All three officials spoke on condition of anonymity because they were not authorized to discuss the investigation publicly.

Tamerlan Tsarnaev was killed in a police shootout Friday. Dzhokhar Tsarnaev was charged Monday with using a weapon of mass destruction to kill, and he could face the death penalty if convicted.

Tamerlan Tsarnaev was an ardent reader of jihadist websites and extremist propaganda, two of the officials said. He frequently looked at extremist sites, including Inspire magazine, an English-language online publication produced by al-Qaida’s Yemen affiliate. The magazine has endorsed lone-wolf terror attacks.

The psychological aspects of radicalization have been studied for years, and while there are some similarities among terrorism cases, there is not a single profile of a violent extremist in the U.S.

Complicating the challenge is that the threat often is rooted in an ideology protected by the Constitution.

Violent extremists can feel caught between two worlds – the one their families left behind to seek better opportunities, and the other in which they feel trapped.

On the Russian social networking site Vkontakte, Dzhokhar Tsarnaev described his world view as “Islam” but his personal goals as “career and money” – a far more capitalistic goal than Muslim teachings that wealth ultimately belongs to God.

“There’s a sort of weird identity crisis,” said Kamran Bokhari, a Toronto-based expert on jihadism and radicalization for the global intelligence company Stratfor. “In many ways, these people are radicalized of extreme religious persuasions in the West that’s not even reflective of what’s back home. So they’re sort of frozen in time, where they’re rejecting the reality in front of them.”

The brothers emigrated in 2002 or 2003 from Dagestan, a Russian republic that has become an epicenter of the Islamic insurgency that spilled over from the region of Chechnya.

It’s still not clear what investigators believe motivated Tamerlan and Dzhokhar to attack.

The brothers’ uncle, Ruslan Tsarni, vehemently dismissed any suggestion that the bombings — which killed three and wounded at least 180 — were motivated by religious views. He called the men “losers” who felt “hatred to those who were able to settle themselves.”

“Anything else to do with religion, with Islam — it’s a fraud, it’s a fake,” Tsarni told reporters. He said someone possibly “radicalized them, but not my brother who just moved back to Russia, who spent his life bringing bread to the table.”

Tsarni also told reporters he hadn’t spoken to his nephews in months.

One of the brothers’ neighbors, Albrecht Ammon, recalled an encounter in which the older brother argued with him about U.S. foreign policy, the wars in Afghanistan and Iraq, and religion.

Ammon said Tamerlan described the Bible as a “cheap copy” of the Quran, used to justify wars with other countries.

“He had nothing against the American people,” Ammon told The Associated Press. “He had something against the American government.”

Dzhokhar, on the other hand, was “real cool,” Ammon said. “A chill guy.”

The cases of homegrown and first-generation terror suspects in the U.S. are few, but the U.S. intelligence community has long been concerned about such potential attackers, particularly the threat posed by people like the Tsarnaev brothers who have no formal terror ties.

“And what makes them especially worrisome is that they’re really difficult for us to detect and, therefore, to disrupt,” Matt Olsen, director of the National Counterterrorism Center, said in June 2011 about homegrown violent extremists.

The U.S. intelligence director’s office has declined to provide official government data on homegrown terrorists, or comment on the Tsarnaev brothers and the investigation into the bombings.

But an August 2011 White House policy paper on countering and preventing violent extremism in the U.S. said that while the numbers remain limited, “violent extremists prey on the disenchantment and alienation that discrimination creates, and they have a vested interest in anti-Muslim sentiment.”

Kenneth Wainstein, who served as the White House homeland security adviser and a top Justice Department lawyer under President George W. Bush, said homegrown and newly immigrated militants develop their extreme views over time and are often borne out of sense of isolation. It’s a problem that has not been as prevalent in the United States as in Europe, which has a larger number of ethnic and nationalist divisions.

“But I think we have seen, over the last few years, some pretty clear and sobering examples of people inspired by overseas terror groups and terror propaganda,” Wainstein said Friday, before Dzhokhar was captured. “They fit more in the category of where you have people who are radicalized here without any apparent connection overseas. A kid can go into his room get radicalized on the Internet without direct connect with anyone overseas, or even without going down the street to the radical preacher. That makes it very hard to detect that person, and poses a significant problem for the intelligence community and law enforcement.”

Investigators also are looking at the six months Tamerlan Tsarnaev spent last year in his ancestral homeland in the predominantly Muslim provinces of Dagestan and Chechnya to see whether he was radicalized by the militants in the area who have waged a low-level insurgency against Russian security forces for years.

While there, he regularly attended a mosque and spent time learning to read the Quran, but “did not fit into the Muslim life,” according to his aunt, Patimat Suleimanova.

She said he seemed more American than Chechen.

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