The brothers behind Monday's deadly bombing at the Boston Marathon are believed to have come to the U.S. from Chechnya as long as a decade ago, but apparently never fit in with the American culture.

“I don’t have a single American friend, I don’t understand them,” the older brother, Tamerlan Tsarnaev, who was killed in a shootout with police hours after the pair was identified as suspects, told a photographer in 2009.

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What drove him and his brother, Dzhokhar A. Tsarnaev, 19, who lived with him in Cambridge, Mass., to perpetrate the deadly attack — which killed three people and injured 176 others — is not clear. They are believed to be Muslim and to have had military training overseas. But the older brother, who was 26, also worked out in a gym and dreamed of making the U.S. Olympic boxing team, according to an online photojournalism slideshow that chronicled his training.

The journalist who created the project, Johannes Hirn, could not be reached for comment. But one caption in his account described the family's odyssey to America.

“Tamerlan fled Chechnya with his family because of the conflict in the early 90s, and lived there for years in Kazakhstan before getting to the United States as a refugee,” read the caption.

Tamerlan previously studied at Bunker Hill Community College for three semesters — fall 2006, spring 2007 and fall 2008 — in hopes of becoming an engineer. He took off a semester from his studies to practice boxing at the Wai Kru Mixed Martial Arts Center in Boston. He also had a three-year-old daughter, his father told Bloomberg TV, and was reportedly arrested in 2009 for domestic assault and battery following an incident involving his girlfriend.

His brother is believed to be the same Dzhokhar Tsarnaev who won a $2,500 scholarship in 2011 from the city of Cambridge, according to online records. Dzhokhar Tsarnaev, who reportedly became a naturalized U.S. citizen on Sept. 11, 2012, later enrolled at the University of Massachusetts Dartmouth.

The father of the suspects, reached in Makhachkala, Russia, characterized his sons as "angels," adding that someone is "playing with them," he told Fox News.

Anzor Tsarnaev said his sons were normal young men who loved people. Earlier Friday, he called on Dzokhar to surrender peacefully, but reportedly warned the United States that “all hell will break loose” if he’ll killed. He told ABC News that he spoke to his sons by phone earlier this week. He said his sons reassured him, saying, "Everything is good, Daddy. Everything is very good."

"Give up. Give up. You have a bright future ahead of you,” Anzor Tsarneav told ABC News. “Come home to Russia.”

He continued: "If they killed him, then all hell would break loose."

An uncle of the brothers, also reached by The Associated Press, said that the men lived together near Boston and have been in the United States for about a decade. They traveled here together from the Russian region near Chechnya, according to Ruslan Tsarni of Montgomery Village, Md.

Tamerlan Tsarnaev, according to a high-ranking law enforcement official, spent six months living in Russia last year. He departed for Russia at the beginning of last year and returned to the United States in mid-2012, the official told FoxNews.com.

Dzhokhar Tsarnaev has never traveled outside the U.S. and applied for asylum and became a naturalized American citizen, the official said.

FoxNews.com's Jana Winter, Joshua Rhett Miller and The Associated Press contributed to this report.