BOSTON — Convicted Boston Marathon bomber Dzhokhar Tsarnaev’s brother frightened at least one relative during a visit to Russia in 2012 when he espoused radical Islamist beliefs, a family member said Monday.

Several of Tsarnaev’s relatives appeared in federal court in Boston to testify at the second phase of his trial, where a jury will determine whether Tsarnaev is sentenced to death for killing three people and wounding 264 in the April 15, 2013, bombing attack on Boston’s best-attended sporting event.

Defense attorneys have been trying to paint the 21-year-old bomber as a secondary player in an attack conceived and led by his 26-year-old brother, Tamerlan Tsarnaev, who died after a gunfight with police four days after the bombing.

Naida Suleimanova, a cousin of the brothers, said she was scared when she learned Tamerlan had adopted extremist views.

“When we were told that he was an adherent of some kind of radical Islam, I was afraid,” Suleimanova said through an interpreter.

“I don’t understand this. Our parents didn’t teach us these things. They taught us to pray and to read the prayers and I am very far away from all this.”

Suleimanova, who appeared to be holding back tears during her testimony, identified Tamerlan’s voice on an audio recording in which he discusses the idea of establishing an Islamic Caliphate with other men, who are not identified.

“I have this rage of hatred inside of me,” Tamerlan said on the recording, according to a translation of the Russian conversation.

Federal prosecutors have cited extremist publications found on Dzhokhar Tsarnaev’s computers, as well as a note in which he suggested the Boston attack was in retribution for U.S. military campaigns in Muslim-dominated countries, as evidence that he wanted “to punish America” with one of the highest-profile attacks on U.S. soil since Sept. 11, 2001.

Martin Richard, 8, Chinese exchange student Lu Lingzi, 23, and restaurant manager Krystle Campbell, 29, died in the bombing. The Tsarnaev brothers shot dead Massachusetts Institute of Technology police Officer Sean Collier three days later.

An aunt of Tsarnaev’s, Patimat Suleimanova, broke down in tears on the witness stand before she began her testimony and was excused to compose herself. Tsarnaev, who has shown little reaction through the course of the two-month trial, was seen dabbing at his eyes as his relatives wept.

Tsarnaev’s father, Anzor Tsarnaev, is Chechen. His mother’s family, the Suleimanovs, are of the Avar ethnicity.

The Tsarnaev family had moved frequently between Dagestan, Siberia, and parts of central Asia before relocating to the United States a decade before the attack, Nadia Suleimanova and her sister, Raisat Suleimanova, testified.

The two said they were surprised when Tsarnaev’s mother, Zubeidat Tsarnaeva, returned to Russia for a visit wearing an Islamic head scarf. Previously she had been a flashy, stylish dresser and not particularly devout, her nieces testified.

“It was a shock for me,” Raisat Suleimanova said through an interpreter. “Knowing what kind of person Zubeidat used to be, it was strange to see that.”

Raisat Suleimanova described Dzhokhar Tsarnaev as having been a “very kind, very warm” child, who was loved by his family.

“I categorically reject what he did,” Suleimanova said. “It’s a great tragedy of course.”

The jury also saw several photos of Dzhokhar as a young boy, including one where Tamerlan carried him on his shoulder.

“Dzhokhar loved his older brother very much,” Naida Suleimanova said. “As is the custom in our families, you would always listen to your older sibling.”