BOSTON (CNN) — The suspects involved in the Boston Marathon bombing were brothers from the Russian Caucasus who moved to Kazakhstan before coming to the United States several years ago, a source briefed on the investigation told CNN.

One of the brothers, identified by several sources as Tamerlan Tsarnaev, 26, studied engineering at Bunker Hill Community College but had taken off a year to train as a boxer, the source said Friday.

The source said a posting on a social media website under his name included the comment: “I don’t have a single American friend. I don’t understand them.”

He died at a hospital overnight after a gun battle with police, authorities said. A source briefed on the investigation says Tsarnaev was wearing explosives and an explosive trigger when his body was recovered.

Several sources identified his brother, who remains on the lam, as Dzhokhar Tsarnaev, 19.

The source briefed on the investigation added that it should not be assumed that the brothers were radicalized because of their origins in the Russian Caucasus.

The spokesman for Chechen President Ramzan Kadyrov said the brothers had not been connected with the Chechen Republic for many years, Russia’s semi-official Interfax news agency reported Friday.

“According to preliminary information, coming from the relevant agencies, the Tsarnaev family moved many years ago out of Chechnya to another Russian region,” press secretary Alvi Kamirov told Interfax. “After that they lived for some time in Kazakhstan, and from there went to the U.S. where the family members received a residence permit. Therefore the individuals concerned did not live as adults in Chechnya.”

Dzhokhar Tsarnaev had worked as a lifeguard at a pool at Harvard University, said George McMasters, who hired him about two and a half years ago and said he was impressed with his work ethic. “He showed up on time, he watched the water, he rotated from position to position fine, got along well with others.”

McMasters, who is the aquatic coordinator, said Tsarnaev gave no clue to a violent side. “He seemed like a very quiet, unassuming young man,” he said. “It is very surprising and shocking to see the destruction that he has brought to the city.”

Last year, McMasters was deployed to Afghanistan with the Army National Guard and, when he returned to the job in August, Tsarnaev was no longer on the staff or the schedule, he said.

Dzhokhar Tsarnaev attended Cambridge Rindge & Latin, a public high school, said Eric Machado, who graduated a year behind the suspect.

“We hung out; we partied; we were good high school friends,” Machado told CNN.

“We’re all, like, in shock. We don’t really understand. There were no telltale signs of any kind of malicious behavior from Dzhokhar. It’s all coming as a shock, really.”

Machado said he lived a block away from the suspect and had not known his older brother.

The campus of the University of Massachusetts – Dartmouth was closed Friday and the school said that one of the suspects was registered as a student at the school.

“Individuals on campus should shelter in place unless instructed otherwise,” the school said in a posting on its website.

“To think that he’s capable of something like this is beyond belief,” Machado said.

Ruslan Tsarni, a Maryland man who said he was an uncle of the suspects, had no sympathy for them and no regret that his elder nephew was killed. “Good,” he told CNN affiliate WBZ. “He got what he deserved.”

Tsarni said Tamerlan Tsarnaev came to the United States as a child in 2000 or 2001, and that he last saw him in 2005 or 2006. “He’s really been a quiet, nice boy,” he said.

CNN’s Clare Sebastian in London contributed to this report