A US jury has sentenced Boston Marathon bomber Dzhokhar Tsarnaev to death for helping carry out the 2013 attack that killed three people and wounded 264 others at the world-renowned race, taking 15 hours to reach a decision.
The federal jury chose death by lethal injection for Tsarnaev, 21, over its only other option: life in prison without possibility of release.
The same panel last month found the ethnic Chechen guilty of placing a pair of homemade pressure-cooker bombs at the race's crowded finish line on 15 April 2013, as well as fatally shooting a policeman.
The bombing was one of the highest-profile attacks on US soil since 9/11 attacks in 2001.
Tsarnaev, dressed in a dark sport coat and light-coloured shirt stood quietly in court as the sentence was read, maintaining the stoic demeanour he had throughout most of the trial.
US District Judge George O'Toole thanked Tsarnaev for his "composure and propriety."
US Attorney General Loretta Lynch, the nation's top law enforcement official, welcomed the jury's decision to sentence Tsarnaev to death.
"The ultimate penalty is a fitting punishment for this horrific crime and we hope that the completion of this prosecution will bring some measure of closure to the victims and their families," Ms Lynch said.
US Attorney for Massachusetts Carmen Ortiz said the jury reached a "fair and just" verdict.
She commended the jurors, whom she said had a "really difficult" job to do, and she told reporters 21-year-old Tsarnaev will pay with his life for what she called a particularly heinous crime and an "act of terrorism."
Reaction outside court from survivors and first responders to the death sentence:
During 10 weeks of testimony, the jury heard from about 150 witnesses, including people whose legs were torn off by the shrapnel-filled bombs.
William Richard, the father of bombing victim Martin Richard, described the gut-wrenching decision to leave his eight-year-old son to die of his wounds so that he could save the life of his daughter, Jane, who lost a leg but survived.
Prosecutors described Tsarnaev as an adherent of al Qaeda's militant Islamist views who carried out the attack as an act of retribution for US military campaigns in Muslim-dominated countries.
Defence attorneys opened the trial on 5 March with the blunt admission that Tsarnaev committed all the crimes he was accused of.
But they argued their client was a junior partner in a scheme hatched and driven by his 26-year-old brother, Tamerlan. Tamerlan died after the gunfight, which ended when Dzhokhar ran him over with a stolen car.
It took the court clerk about 20 minutes to readout the 24-page verdict form, which covered the aggravating factors that prosecutors argued justified a death sentence and the mitigating factors the defence said suggested a life sentence, before he announced the actual sentence to the silent, packed courtroom.
The jurors accepted the bulk of the prosecution's aggravating factors, unanimously finding that Tsarnaev had not demonstrated remorse for his actions.
They rejected many of the mitigating factors, with only three of the 12 jurors believing the defence's claim that Tsarnaev had acted under his older brother's influence.
The jury's decision does not mean that death is imminent for the former high school wrestler.
Judge O'Toole will formally sentence Tsarnaev to death at a yet-to-be-scheduled hearing sometime in the next few months. Defence attorneys are likely to appeal the decision.
