Three people were killed and more than 260 injured when two homemade pressure cooker bombs exploded near the finish line of the race.
Tsarnaev launched the attack with his brother Tamerlan, with the couple then on the run.
Four days after the bombing, Tamerlan was pronounced dead at the scene of a shootout with police after his younger brother inadvertently ran him over with a car.
Six months after arguments were heard in the case, a three-judge panel of the 1st U.S. Circuit Court of Appeals in Boston ordered a new trial on the sentence he should receive.
“But make no mistake: Dzhokhar will spend his remaining days locked in prison, the only question remaining is whether he will die by execution,” the judges said.
In 2015, Tsarnaev was convicted of 30 counts, including conspiracy and the use of a weapon of mass destruction.
Judge Ojetta Rogeriee Thompson said Friday that the trial judge “failed” to conduct the jury selection process and to screen jurors for possible bias following publicity prior to the trial surrounding the case. publicized.
Krystle Campbell’s mother, who was killed in the attack, has expressed outrage at the latest court ruling.
“I just don’t understand,” Patricia Campbell told the Boston Globe.
“It’s just terrible that he’s allowed to live his life. It is unfair. He didn’t wake up one morning and decided to do what he did. He planned it. He did a vicious and ugly thing.
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President Donald Trump was also critical, saying, “I see in Boston, where you have the animal that killed so many people during the Boston Marathon.
“They just sent this death sentence back to the lower courts for a long debate. It’s ridiculous. ”
Tsarnaev’s lawyers argued that intense media coverage meant he was unable to get a fair trial in Boston.
They also cited social media posts from two jurors suggesting they had strong opinions on the case before the trial began in 2015.
Tsarnaev’s lawyers said one of the jurors, who would later become the jury foreman, posted dozens of tweets in the wake of the bombing.
A post after Tsarnaev’s capture called it “garbage”.
He is serving his sentence in a super-max high-security Colorado prison.