Boston Marathon bomber Dzhokhar Tsarnaev has been sentenced to die by lethal injection for the 2013 attack that killed three people and injured 264.
The U.S. jury in Massachusetts reached the decision Friday after more than 14 hours of deliberations over three days.
The 21-year-old Tsarnaev was convicted last month of all 30 U.S. federal charges against him, 17 of which carried the possibility of the death penalty.
He showed no reaction as the jury sentenced him to death, his head down slightly and his hands folded in front of him.
The defence asked that the jury be polled, and each confirmed that the verdict represented his or her decision.
The sentence came down exactly 25 months after the April 15, 2013, bombings.
Tsarnaev killed a Massachusetts Institute of Technology police officer days later.
The defence sought to save Tsarnaev's life by pinning most of the blame on his radicalized older brother, Tamerlan.
But prosecutors portrayed Tsarnaev as an equal partner in the attack and so heartless he placed a bomb behind children, killing an eight-year-old boy.
'A fitting punishment'
The jury reached a "fair and just" verdict, the U.S. attorney for Massachusetts Carmen Ortiz said.
"Now he will go away and we will be able to move on. Justice. In his own words, 'an eye for an eye,"' said bombing victim Sydney Corcoran, who nearly bled to death and whose mother lost both legs.
Karen Brassard, who suffered shrapnel wounds on her legs, said: "We can breathe again."
Richard Donohue, a transit police officer who was badly wounded during the manhunt that followed the bombing, said,
"The verdict, undoubtedly a difficult decision for the jury, gives me relief and closure as well as the ability to keep
"Today, more than ever, we know that Boston is a city of hope, strength and resilience, that can overcome any challenge."
U.S. Attorney General Loretta Lynch reacted to the death sentence by saying "the ultimate penalty is a fitting punishment for this horrific crime."
Tsarnaev's father, Anzor Tsarnaev, reached by phone by the Associated Press in the Russian region of Dagestan, let out a deep moan upon hearing the news and hung up.
Killed in the bombing were Lingzi Lu, a 23-year-old Boston University graduate student from China; Krystle Campbell, a 29-year-old restaurant manager from Medford; and eight-year-old Martin Richard, who had gone to watch the marathon with his family. Massachusetts Institute of Technology police officer Sean Collier was shot to death in his cruiser days later. Seventeen people lost legs in the bombings.
Tamerlan Tsarnaev died days after the bombing when he was shot by police and run over by Dzhokhar during a chaotic getaway attempt.
In deciding on the death penalty, the jury had to fill out a detailed, 24-page worksheet in which they tallied up the so-called aggravating factors and mitigating factors.
The possible aggravating factors cited by the prosecution included cruelty of the crime, the killing of a child, the amount of carnage inflicted, and any lack of remorse. The possible mitigating factors included his age, the possible influence of his brother and his turbulent, dysfunctional family.
The jury agreed with the prosecution on 11 of the 12 aggravating factors they cited, including a lack of remorse. In weighing possible mitigating factors, only three of the 12 jurors found he acted under the influence of his brother.
Tsarnaev did not take stand
Tsarnaev did not take the stand at his trial, and he slouched in his seat through most of the case, a seemingly bored look on his face. In his only flash of emotion during the months-long case, he cried when his Russian aunt took the stand.
The only evidence of any remorse on his part in the two years since the attack came from the defence's final witness, Sister Helen Prejean, a Roman Catholic nun and staunch death penalty opponent made famous by the movie Dead Man Walking.
She quoted Tsarnaev as saying of the bombing victims: "No one deserves to suffer like they did."
Tsarnaev's lawyers also called teachers, friends and Russian relatives who described him as a sweet and kind boy who cried during The Lion King. The defence called him a "good kid."
The defence argued that sparing his life and instead sending him to the federal Supermax prison in Florence, Colo., would be a harsh punishment and would best allow the bombing victims to move on with their lives without having to read about years of death penalty appeals.
U.S. District Judge George O'Toole Jr. will formally impose the sentence at a later date during a hearing in which bombing victims will be allowed to speak. Tsarnaev will also be given the opportunity to address the court.
With files from CBC News and Reuters