Dzhokhar Tsarnaev's convictions leave the jury only two options: death penalty or life without parole.

AFP/New York

Convicted Boston bomber Dzhokhar Tsarnaev is a remorseless terrorist who deserves to die for killing innocent Americans in the name of politics, prosecutors told jurors at the end of his trial on Wednesday.

The 21-year-old former student was found guilty last month of carrying out the April 15, 2013 bombings that killed three people and wounded 264 in one of the deadliest attacks in the US since 9/11.

The immigrant of Chechen descent was convicted on all 30 counts related to the bombings at the Boston Marathon, and the subsequent murder of a police officer, a carjacking and a shootout while on the run.

Tsarnaev's convictions leave the jury only two sentencing options under federal law: the death penalty or life without parole.

"His actions have earned him a sentence of death," assistant US attorney Steve Mellin told the jury in the government's closing statement as Tsarnaev sat immobile, staring at the table in front of him.

Mellin quoted from a bloodied message that Tsarnaev wrote to justify the attacks over America's wars in Iraq and Afghanistan before he was arrested, in a parked boat, four days after the attacks.

"No remorse, no apology. Those are the words of a terrorist convinced he has done the right thing. He felt justified in killing, maiming and seriously injuring innocent men, women and children," Mellin said.

Harrowing testimony

The prosecutor recalled harrowing testimony from the loved ones of those who were killed, saying they will never recover from their loss.

He reminded jurors of the brutal injuries that Tsarnaev inflicted, showing the packed court room photographs of the victims happy and smiling in the days and years before the attacks.

The defence, which will make its closing arguments later Wednesday, has sought to portray Tsarnaev's 26-year-old older brother as the mastermind of the attacks who manipulated a frightened younger brother.

It has presented 21 mitigating factors, including Tsarnaev's young age, 19 at the time, his brother's domineering influence, his father's mental illness, his parents return to Russia in 2012 and testimony that he is remorseful.

Tsarnaev's older brother Tamerlan was killed in a shootout with police, leaving his brother to face punishment alone.

Jurors may also consider that his friends and teachers knew him to be hard-working and considerate, and "still care for him," the judge said Wednesday, and that his "aunts and cousins love and care for him."

Earlier on Wednesday the judge delivered nearly an hour and a half of lengthy instructions to the same jury, who convicted Tsarnaev in April and who must now choose between the death penalty or life imprisonment.

"The choice between these very serious alternatives is yours and yours alone to make," Judge George O'Toole said.