A US jury has decided Dzhokhar Tsarnaev should die for his role in the Boston Marathon bombing in April 2013.

The sentence on Friday came after 14 hours of deliberations on whether Tsarnaev, who was a teenager when he carried out the attacks with his elder brother, Tamerlan, should be imprisoned for the rest of his life or be executed.

The 21-year-old did not react when the sentence was read out, the Associated Press reported.

Tsarnaev was convicted last month of all 30 federal charges against him, 17 of which carried the possibility of the death penalty.

Three people were killed and more than 260 were injured when two pressure-cooker bombs, packed with shrapnel, exploded near the marathon finish line on April 15, 2013.

Dzhokar and Tamerlan also killed a Massachusetts Institute of Technology police officer days later.

Tsarnaev’s lawyer, Judy Clarke, admitted from the beginning that his client participated in the bombings, bluntly telling jurors in her opening statement, “It was him.”

But the defence sought to show that most of the blame for the attack fell on his older brother, who wanted to punish the US for its actions in Muslim countries.

They said Dzhokhar was an impressionable 19-year-old, who fell under the influence of a brother he admired.

Prosecutors portrayed Tsarnaev as an equal partner in the attack, saying he was so heartless he put a bomb behind a group of children, killing an eight-year-old boy.

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