BOSTON (AP) — A federal appeals court has ordered the judge who oversaw Boston Marathon bomber Dzhokhar Tsarnaev’s trial to investigate the defense’s claims of juror bias and determine whether his death sentence should stand.

The Boston-based 1st U.S. Circuit Court of Appeals did not throw out Tsarnaev’s death sentence on Thursday.

Defense lawyers had pushed for that while claiming bias by two people who sat on the jury that convicted Tsarnaev for his role in the bombing that killed three people and injured hundreds near the marathon’s finish line in 2013.

But the appeals court found that the trial judge did not adequately probe Tsarnaev’s claims of juror bias, and sent the case back to the judge for a new investigation.

The U.S. attorneys office in Massachusetts declined to comment.