By Elizabeth Barber

BOSTON (Reuters) - The older of the two brothers in the Boston Marathon bombing was a controlling boyfriend who terrified his future wife's friends but held great influence in his family, witnesses testified as lawyers fought to save the younger brother's life.

Tamerlan Tsarnaev, 26, died four days after the April 15, 2013 attack that killed three people and injured 264. His younger brother, Dzhokhar Tsarnaev, last month was convicted of carrying out the attack and could be sentenced to death.

Defense lawyers on Tuesday continued to call witnesses to make their case that the surviving brother, 21, should be sentenced to life in prison without possibility of release rather than death for carrying out one of the highest-profile attacks on U.S. soil since Sept. 11, 2001.

The lawyers, who at the trial's opening in March conceded that Dzhokhar Tsarnaev had committed all the crimes of which he was accused, contend that Tamerlan was the driving force behind the bombing, with his younger brother going along out of a sense of sibling loyalty.

The jury also heard testimony that the Tsarnaevs' father, Anzor, was mentally ill and that the oldest healthy male in any family of the Tsarnaevs' Chechen ethnicity was expected to lead and be obeyed.

Amanda Ransom, 25, told jurors that her college friendship with Katherine Russell, Tamerlan's widow, unraveled as the couple's relationship grew more serious.

Tamerlan was an outgoing, flashy dresser when he began dating Russell, Ransom said. She became concerned after Tamerlan cheated on Russell and laughed after tricking her into believing she might have contracted AIDS from him.

"At one point I heard him laughing really hard, and she was crying," Ransom testified, referring to the AIDS incident. Tamerlan did not have AIDS, she said.

Russell, who was not raised Muslim, began wearing an Islamic hijab as her relationship with Tamerlan became more serious and distanced herself from her friends, said Ransom, who shared an apartment with her. Ransom said she ultimately moved out of the apartment in the dead of the night after Tamerlan threatened her when she tried to intervene in a fight between the two.


Prior witnesses called by the defense have testified that Dzhokhar Tsarnaev was unlike his aggressive brother, growing from a happy child into an easygoing young man who liked Domino's pizza and rap music.

The father, Anzor Tsarnaev, suffered from seizures, post-traumatic stress disorder and believed he was being tailed by Russian spies, said Alexander Niss, a psychiatrist who treated him from 2003 through 2005.

"He was a very sick guy," Niss said, adding that the father's illnesses were so debilitating that he could neither drive nor work.

That made Dzhokhar all the more subservient to Tamerlan, said Michael Reynolds, an associate professor of Near Eastern studies at Princeton University, who provided expert testimony on Chechen culture.

"The younger brother owes his deference to the older brother," he said.

Assistant U.S. Attorney William Weinreb questioned the relevance of Tsarnaev's ethnicity, noting that neither of the brothers was born in Chechnya and that Dzhokhar, who spent much of his life in Russia before moving to the United States a decade before the attack, had never lived there.

"Are you here to say that a Chechen terrorist is less morally culpable for their crimes?" asked Weinreb.

"No," Reynolds replied.

Federal prosecutors earlier presented evidence showing that Tsarnaev's computers contained radical jihadist literature, including copies of al Qaeda's "Inspire" magazine, and noted that he left a note suggesting the attack was an act of retribution for U.S. military campaigns in Muslim-dominated countries.

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.

(Editing by Scott Malone and Dan Grebler)