Last Updated May 5, 2015 3:08 PM EDT
BOSTON -- Boston Marathon bomber Dzhokhar Tsarnaev's lawyers called a Russian historian and a psychiatrist to the stand Tuesday in a bid to save the Boston Marathon bomber from the death penalty by portraying him as the product of a dysfunctional family from a turbulent corner of the world.
Dr. Alexander Niss, a psychiatrist who treated Tsarnaev's father from 2003 to 2005, said he diagnosed the elder Tsarnaev with post-traumatic stress disorder after he reported being tortured in a Russian camp during the Chechen wars with Russia in the 1990s.
Niss said Anzor Tsarnaev, a Chechen, showed typical symptoms of PTSD, including anxiety, panic attacks, flashbacks and paranoia. He said Tsarnaev also complained of headaches, dizziness, nosebleeds and other physical ailments, and during one phase of his treatment, was going to the emergency room almost every day.
"He was a sick guy," Niss said.
Niss took the stand during the penalty phase of Dzhokhar Tsarnaev's trial, during which the jury will decide whether the 21-year-old former college student should get the death penalty or life in prison for the 2013 bombing that killed three people and wounded more than 260. A recent poll showed a majority of Bostonians are against Tsarnaev paying with his life.
The defense told jurors earlier that both of Tsarnaev's parents were diagnosed with mental illness.
Tsarnaev's lawyers are hoping his background - combined with their claim that he was heavily influenced by his radical older brother, Tamerlan - will convince the jury he does not deserve a death sentence. Tamerlan, 26, was killed days after the bombing during a getaway attempt.
Dzhokhar Tsarnaev lived in the former Soviet republic of Kyrgyzstan and the Dagestan region of Russia, bordering Chechnya, before moving to the U.S. in 2002. He was 19 at the time of the marathon bombing.
The defense also called as a witness Michael Reynolds, a Princeton University professor who described the North Caucasus region of Russia, including Chechnya, a mountainous area of southern Russia where Tsarnaev's father's family has roots.
Reynolds gave a history of the region, including its centuries of conflict with Russia. He said Chechen families are very patriarchal, with the father or oldest son having the clear role as the decision-maker for the family.
"It's expected that the younger brother will listen to the older brother," he said.
During cross-examination, prosecutor William Weinreb pointed out that Dzhokhar and Tamerlan spent little or no time living in Chechnya. Dzhokhar was 8 when he moved to the U.S.
Weinreb also said Dzhokhar smoked cigarettes and marijuana and drank alcohol despite admonitions from Tamerlan.
On Monday, for the first time since his trial began four months ago, Tsarnaev dropped his blank expression and wept as his Russian aunt sobbed uncontrollably on the stand. He grabbed a tissue and repeatedly dabbed his eyes and cheeks.
Five Russian relatives - three cousins and two aunts - took the stand for the defense Monday, portraying Tsarnaev as a kind and gentle child who cried while watching "The Lion King." The relatives had not seen Tsarnaev since he was 8.
"I think that his kindness made everybody around him kind," his cousin Raisat Suleimanova said through a Russian translator.
Federal prosecutor William Weinreb pounced, asking her if she believes a deadly attack on innocent civilians can be considered kind. Tsarnaev's lawyer objected, and Suleimanova was not allowed to answer the question.