Boston Marathon bombing trial
David Bruck (L), Timothy Watkins (C) and Judy Clarke, defense attorneys for Boston Marathon bomber Dzhokhar Tsarnaev, leave the courthouse following the first day of the defense's presentation in the penalty phase of the trial in Boston, Massachusetts, United States April 27, 2015.Reuters

Lawyers of convicted Boston Marathon bomber Dzhokhar Tsarnaev began their case on 27 April in a quest to save his life. The defence will have to convince jurors that Tsarnaev was following his brother Tamerlan's radicalised ways and that he deserves life in prison, not death row.

Prosecutors took their turn during the sentencing phase last week, calling on bombing victims to testify about their injuries and life after the 2013 Boston Marathon. Now it will be up for Tsarnaev's attorneys to humanize the 21-year-old and pin the bombings on his now-deceased older brother.

Several members of Tsarnaev's family have arrived in Boston and are expected to take the stand in effort to save him.

One of Tsarnaev's lawyers, David Bruck, said that the convicted killer cannot receive a punishment equal to the victims' suffering during opening statements . "There is no point in trying to hurt him as he hurt because it can't be done," Bruck said, according to the Associated Press.

Bruck also addressed the photo of Tsarnaev giving the middle finger to a security camera in prison, saying it was the action of an "immature 19-year-old." The photo, which caused a stir when it was released by prosecutors last week, was taken three months after the April 2013 attacks that left three dead and injured over 260.

For their first witness, the defence called on Imam Loay Assaf, who recalled an instance when Tamerlan Tsarnaev became enraged during prayer services. According to Assaf, Tamerlan interrupted the service when Assaf compared Martin Luther King Jr to the Prophet Muhammad.

Another witness, Robert Barnes, testified that Tamerlan criticised the US government and its involvements abroad months before the bombings in Boston.

Bomber's mother-in-law called to testify

The defence called on Tamerlan's mother-in-law Judith Russell to testify as well, the AP reported. Russell told the jury that she and her husband disapproved of their daughter's relationship with Tamerlan. The elder Tsarnaev brother later married Katherine Russell and the two had a daughter.

Katherine Russell's friend Gina Crawford was one of the last to testify on Monday. Crawford said that Russell texted her the day of attacks and told her that Tamerlan was at home at the time of the bombings. However, Russell added that "a lot more people are killed every day in Syria and in other places".

Dzhokhar Tsarnaev was convicted of 30 federal charges for his involvement in the twin bombings at the 2013 Boston Marathon and the subsequent killing of MIT police officer Sean Collier. Seventeen of those charges carry the death penalty. The sentencing phase is expected to last at least four weeks.