The Boston Marathon bomber, Dzhokhar Tsarnaev, 21, was sentenced to death by a U.S. jury Friday about 3:30 p.m ET for helping in the 2013 attack that killed three people and wounded 264 others.

The case on the Boston Marathon bomber was received by the jury Wednesday. They deliberated for 15 hours, after which reaching its verdict - death by lethal injection,reports NBC News.

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The other option was life in prison without possibility of release.

After the verdict was announced, Tsarnaev said nothing. He was seen sitting in his chair, remaining expressionless while U.S. District Judge George O'Toole thanked the jury.

Throughout the ordeal on deciding the fate of the Boston Marathon bomber, the mood in the courtroom remained heavy and subdued. Before the trial started, the judge's clerk, Paul Lyness, admonished those inside that "any outbursts" would be treated as contempt of court, according to ABC News. There hed been none.

The same who decided Tsarnaev's fate also found him guilty last month for placing homemade pressure-cooker bombs on April 15, 2013 and fatally shooting a policeman.

The Boston Marathon bombing is considered one of the highest-profile attacks on U.S. soil since the Sept. 11, 2001 attack on the World Trade Center.

There had been 10 weeks of testimony, during which jurors heard from about 150 witnesses.

Tsarnaev was described by prosecutors as an ethnic Chechen, a supporter of al Qaeda's militant Islamist views which does attacks as retribution for U.S. military campaigns in Muslim countries.

Despite the decision Friday on the Boston Marathon bomber, it is not tantamount to Tsarnaev facing imminent death. Defence attorneys are still likely to appeal the sentence, which could still take years, according to Reuters.

"I know that there is still a long road ahead," according to survivor Karen Brassard. "There are going to be many, many dates ahead. But today we can take a breath, and actually breathe again," she told reporters.

The death penalty is still highly controversial in Massachusetts despite the Boston Marathon bomber's verdict. In Boston and across Massachusetts, there is reportedly an aversion towards capital punishment, which had been banned in the state in 1984. No convict had been executed there since 1947.

There are polls showing that many residents around Boston are opposed to killing Tsarnaev. Last month, a poll by the Boston Globe showed that fewer than 20 percent of state residents favored death for Tsarnaev.

However, Tsarnaev was tried under federal law, thus allowing for lethal injection to be a punishment.

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