To most, they seemed ordinary American boys

With their baseball hats and sauntering gaits, they appeared to friends and neighbors like ordinary American boys. But the Boston bombings suspects were refugees from another world - the blood, rubble, and dirty wars of the Russian Caucasus.

Tamerlan Tsarnaev, 26, was a southpaw heavyweight boxer who represented New England in the National Golden Gloves and talked about competing on behalf of the United States. His tangle-haired, 19-year-old brother, Dzhokhar, was a skateboarder who listened to rap and seemed easygoing to other kids in his Cambridge, Mass., neighborhood.

Tamerlan is now dead, killed in a shootout with police. Dzhokhar was taken into custody Friday evening after a manhunt that left the city virtually paralyzed. And hidden behind their former lives in Massachusetts is a biography containing old resentments that appeared to have mutated into radical Islamic violence.

The brothers who are alleged to have planted bombs Monday near the finish line of the Boston Marathon reached the United States in 2002 after their ethnic Chechen family fled the Caucasus. They had been living in the Central Asian republic of Kyrgyzstan and were prevented from resettling in war-racked Chechnya.

In speaking about his boxing career in 2009, Tamerlan told a photographer that in the absence of an independent Chechnya, he would rather compete for the United States than for Russia, a hint that past troubles were not forgotten. He appeared increasingly drawn to radical Islam. On a YouTube channel, he recently shared videos of lectures from a radical Islamic cleric; in one, voices can be heard singing in Arabic as bombs explode.

His younger brother, who was widely known as "Jahar," may have followed in his footsteps.

While terrorists from the Caucasus have struck in Moscow and other parts of Russia, the conflict in the region has never led to attacks in other countries. One possible explanation for the Boston bombing, said Aslan Doukaev, an expert on the Caucasus who works for Radio Liberty in Prague, is that the brothers were motivated by radical jihadism, not Chechen separatism.

As the war in Chechnya wound down after Russian forces withdrew - they left formally in 2009 - violence has spilled into neighboring republics such as Dagestan, where the Tsarnaev family once found shelter and where the brothers' parents now live. Tamerlan visited Dagestan last year, said an official with knowledge of his travels.

Tamerlan studied accounting at Bunker Hill Community College from 2006 to 2008, said a college spokesperson. He was married to Katherine Russell, 23, and the couple had a baby daughter, according to neighbors.

In 2011, Dzhokhar graduated high school, where he was the captain of the wrestling team, and went on to study at the University of Massachusetts. He hoped to become a dentist.

Ruslan Tsarni, the uncle of the suspected bombers, said he was ashamed of them. Asked what provoked his nephews, he replied: "Being losers - hatred to those who were able to settle themselves."

"We are Muslim. We are ethnic Chechens," he told reporters outside his house in Montgomery Village, Md. "Somebody radicalized them, but it was not my brother. . . . Of course, we are ashamed."