BOSTON – A jury sentenced Dzhokhar Tsarnaev to death Friday for the Boston Marathon bombing, sweeping aside pleas that he was just a “kid” who fell under the influence of his fanatical older brother.

Tsarnaev, 21, stood with his hands folded, his head slightly bowed, upon learning his fate, sealed after 14 hours of deliberations over three days. It was the most closely watched terrorism trial in the U.S. since the Oklahoma City bombing case two decades ago.

The decision sets the stage for what could be the nation’s first execution of a terrorist in the post-9/11 era, though the case is likely to go through years of appeals. The execution would be carried out by lethal injection.

“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.

Michael Ward, a firefighter who came to the rescue of the attack’s victims, said: “He wanted to go to hell, and he will get there early.”

Three people were killed and more than 260 wounded when Tsarnaev and his brother set off two shrapnel-packed pressure-cooker bombs near the finish line of the race on April 15, 2013. The Tsarnaevs also shot an MIT police officer to death during their getaway.

The 12-member federal jury had to be unanimous for Tsarnaev to get the death penalty. Otherwise, the former college student would have automatically received a sentence of life in prison with no chance of parole.

In weighing the arguments for and against death, the jurors decided, among other things, that Tsarnaev showed a lack of remorse. And they emphatically rejected the defense’s central argument – that he was led down the path to terrorism by his big brother.

“Today the jury has spoken. Dzhokhar Tsrnaev will pay for his crimes with his life,” said U.S. Attorney Carmen Ortiz.

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. Tsarnaev’s lawyers had no comment as they left the courtroom.

The attack and the ensuing manhunt paralyzed the city for days and cast a pall over the marathon – normally one of Boston’s proudest, most exciting moments – that has yet to be lifted.

With Friday’s decision, community leaders and others talked of closure, of resilience, of the city’s Boston Strong spirit.

“Today, more than ever, we know that Boston is a city of hope, strength and resilience that can overcome any challenge,” said Mayor Marty Walsh.

Tsarnaev was convicted last month of all 30 charges against him, including use of a weapon of mass destruction. Seventeen of those charges carried the possibility of a death sentence.

Tsarnaev’s chief lawyer, death penalty specialist Judy Clarke, admitted at the very start of the trial that he participated in the bombings, bluntly telling the jury: “It was him.”

But the defense argued that Dzhokhar was an impressionable 19-year-old who was led astray by his volatile and domineering 26-year-old brother, Tamerlan. He was portrayed as the mastermind of the plot to punish the U.S. for its wars in Muslim countries.

Tamerlan died days after the bombing when he was shot by police and run over by Dzhokhar during a chaotic getaway attempt.

Prosecutors depicted Dzhokhar Tsarnaev as an equal partner in the attack, saying he was so coldhearted he planted a bomb on the pavement behind a group of children, killing an 8-year-old boy.

To drive home their point, prosecutors cited the message he scrawled in the dry-docked boat where he was captured: “Stop killing our innocent people and we will stop.” And they opened their case in the penalty phase with a startling photo of him giving the finger to a security camera in his jail cell months after his arrest.

“This is Dzhokhar Tsarnaev –unconcerned, unrepentant and unchanged,” prosecutor Nadine Pellegrin said.

The jurors also heard grisly and heartbreaking testimony from numerous bombing survivors who described seeing their legs blown off or watching someone next to them die.

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 8-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.

The speed with which the jury reached a decision surprised some, given that the jurors had to fill out a detailed, 24-page worksheet in which they tallied up the factors for and against the death penalty.

The possible aggravating factors included the cruelty of the crime, the killing of a child, the amount of carnage and lack of remorse. The possible mitigating factors included Tsarnaev’s age, the influence of his brother, and his turbulent, dysfunctional family.

The jury agreed with the prosecution on 11 of the 12 aggravating factors cited. In weighing the mitigating factors, only three of the 12 jurors found Tsarnaev acted under the influence of his brother.

Tsarnaev did not take the stand at his trial, and he slouched 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 defense’s final witness, Sister Helen Prejean, a Roman Catholic nun and staunch death penalty opponent portrayed in the movie “Dead Man Walking.”

She quoted Tsarnaev as saying of the 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 defense called him a “good kid.”

The defense argued that sparing his life and sending him instead to the high-security Supermax federal prison in Colorado would be a harsh punishment and would help the victims move on with their lives without having to read about years of death row appeals.

The outcome of the penalty phase was wrapped in high suspense.

Massachusetts is a staunchly anti-death penalty state that hasn’t executed anyone since 1947, and there were fears that a death sentence for Tsarnaev would only satisfy his desire for martyrdom. Even the grieving parents of the 8-year-old boy publicly urged prosecutors to drop their push for death.

But others argued that if capital punishment is to be reserved for the “worst of worst,” Tsarnaev qualifies.

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.

The Tsarnaevs – ethnic Chechens – lived in the former Soviet republic of Kyrgyzstan and the volatile Dagestan region, near Chechnya, before moving to the U.S. about a decade before the bombings. They settled in Cambridge, just outside Boston.