Dzhokhar Tsarnaev’s lawyers argued the intense media coverage meant it was impossible for him to have a fair trial in Boston.
Boston Marathon bomber Dzhokhar Tsarnaev has had his death sentence for the 2013 attack overturned by a US federal appeals court.
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 pair then going on the run.
Four days after the bombing, Tamerlan was pronounced dead at the scene of a gun battle 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 US Circuit Court of Appeals in Boston has ordered a new trial over what sentence he should receive.
“But make no mistake: Dzhokhar will spend his remaining days locked up in prison, with the only matter remaining being whether he will die by execution,” the judges said.
In 2015, Tsarnaev was convicted on 30 charges, including conspiracy and use of a weapon of mass destruction.
Judge Ojetta Rogeriee Thompson said on Friday the trial judge “fell short” in conducting the jury selection process and screening jurors for potential bias following pre-trial publicity surrounding the high-profile case.
The mother of Krystle Campbell, who was killed in the attack, expressed outrage at the latest court decision.
“I just don’t understand it,” Patricia Campbell told The Boston Globe.
“It’s just terrible that he’s allowed to live his life. It’s unfair. He didn’t wake up one morning and decide to do what he did. He planned it out. He did a vicious, 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 conviction for the death penalty back to the lower courts so they’ll argue about that for a long time. It’s ridiculous.”
Tsarnaev’s lawyers argued the intense media coverage meant it was impossible for him to have a fair trial in Boston.
They also cited social media posts from two jurors suggesting they harboured strong opinions on the case before the trial got under way in 2015.
Tsarnaev’s lawyers said one of the jurors, who would later become the jury’s foreperson, posted dozens of tweets in the wake of the bombing.
One post after Tsarnaev was captured called him a “piece of garbage”.
He is serving his sentence in a high-security supermax prison in Colorado.