Boston bomber's sentencing trial on death penalty begins Tuesday

Prosecutors and defence attorneys for convicted Boston Marathon bomber Dzhokhar Tsarnaev on Tuesday will begin making their cases on whether or not he should be sentenced to death for the 2013 attack and its aftermath.

Tsarnaev, a 21-year-old ethnic Chechen, was found guilty on April 8 of killing three people and injuring 264 at the marathon finish line and fatally shooting a police officer as he and his older brother, Tamerlan, prepared to flee three days later.

Citing al Qaeda materials found on his laptop and a note in which he suggested the April 15, 2013 bombing was an act of retribution for US military campaigns in Muslim-dominated countries, federal prosecutors sought to paint Tsarnaev as a violent extremist.

But defence attorneys countered that 26-year-old Tamerlan, who died following a gunfight with police hours after the officer's slaying, was the driving force behind the attacks, with Dzhokhar acting in a secondary role out of a sense of sibling loyalty.

US District Judge George O'Toole blocked the defence from introducing much evidence about Tamerlan in the trial's first phase, but legal experts said Tsarnaev's attorneys will likely have much freer rein in the sentencing phase.

It begins with opening statements from prosecutors and defence attorneys, who will then call witnesses over about four weeks. When the witness testimony ends, the same jury that convicted Tsarnaev will decide on the death sentence or life in prison without the possibility of parole. The judge ordered jurors to stay away from events marking the second anniversary of the attack and Monday's 119th running of the Boston Marathon.

The idea of putting Tsarnaev to death is controversial in Boston. Massachusetts state law does not allow for capital punishment, which is an option in this case because Tsarnaev was tried in federal court.

Most Boston-area residents oppose putting Tsarnaev to death than support it, according to opinion polls. Over the past week, several people whose family members were killed, or survivors who lost limbs in the attack, have spoken out against the death penalty for Tsarnaev.

They argued that a deal in which Tsarnaev was sentenced to life in prison without possibility of parole in exchange for giving up his appeal rights would spare victims, their families and the city of Boston from sitting through several more weeks of emotionally draining testimony and possibly years of appeals.