BOSTON (AP) — A federal appeals court Friday threw out Dzhokhar Tsarnaev’s death sentence in the 2013 Boston Marathon bombing, saying the judge who oversaw the case did not adequately screen jurors for potential biases.

A three-judge panel of the 1st U.S. Circuit Court of Appeals ordered a new penalty-phase trial on whether the 27-year-old Tsarnaev should be executed for the attack that killed three people and wounded more than 260 others.

“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,” Judge O. Rogeriee Thompson wrote in the ruling, more than six months after arguments were heard in the case.

Prosecutors could ask the full appeals court to hear the case or go straight to the U.S. Supreme Court.

The mother of Krystle Campbell, the 29-year-old killed in the attack, expressed outrage at the court’s 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.”

Former Massachusetts Bay Transportation Authority officer Dic Donohue, who was severely injured in a gunfight with the brothers, said the ruling was not surprising to him.

Tsarnaev’s lawyers acknowledged at the beginning of his trial that he and his older brother, Tamerlan Tsarnaev, set off the two bombs at the marathon finish line. But they argued that Dzhokar Tsarnaev is less culpable than his brother, who they said was the mastermind behind the attack.