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BOSTON (CNN & AP) — Friends of Dzhokar Tsarnaev told CNN that Tsarnaev sent out tweets after the Monday bombing that are now being analyzed for their meaning.

His tweets included one early Wednesday at 1:43 a.m. that read, “I’m a stress free kind of guy.”

On April 15 at 8:04 p.m. — hours after the bombings — he tweeted a quote from rapper Jay-Z, “Ain’t no love in the heart of the city, stay safe people.”

Eric Mercado, who said he is a friend of Dzhokhar, told reporters when he first saw the video released by the FBI, he and his friends joked about it only looking like Dzhokhar.

“It was kind of a joke amongst friends,” he said. “‘Oh, that’s Dzhokhar.’ No one wants to believe that their friend from high school is a quote, ‘terrorist'” Mercado said.

He said Dzhokhar’s hat was a signature look for him.

“The hat was a signature, turned backwards on his head, always,” he said.

According to the Associated Press, the father of Dzhokhar Tsarnaev, 19, called him ‘an angel and an intelligent boy.’ Anzor Tsarnaev spoke to an AP reporter by telephone on Friday and said his son is a second-year medical student.

The suspects involved in the Boston Marathon bombing are brothers from the Russian Caucasus who moved to Kazakhstan before coming to the United States several years ago. The younger Tsarnaev became a U.S. citizen on September 11, 2012, a federal official said Friday. That’s the 11th anniversary of the al Qaeda attacks on the United States.

The older brother, killed overnight in a shootout with police, was identified by sources as Tamerlan Tsarnaev, 26. He reportedly studied engineering at Bunker Hill Community College but had taken off a year to train as a boxer, the source said. He reportedly wanted to compete on the U.S. Olympic boxing team.

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

He was shot several times by police overnight and taken to a hospital where he died.

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 Caucusus.

Dzhokhar Tsarnaev attended Cambridge Rindge & Latin, a public high school, said Eric Machado, who graduated a year behind the suspect, who he said had worked at Harvard University as a lifeguard.

“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 — and that Dzhokhar had attended the University of Massachusetts — Amherst.

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