The 1st U.S. Circuit Court of Appeals in Boston has overturned the death sentence of 2013 Boston Marathon bomber Dzhokhar Tsarnaev. His conviction has been upheld and a new trial is set to determine a different sentence.

Tsarnaev and his brother, Tamerlan, planted two bombs near the finish line of the Boston Marathon, which killed three people and injured more than 260 others. His brother was killed in a shootout with police on April 19, 2013.

In 2015, Tsarnaev was convicted and sentenced to death on 30 charges, including conspiracy and use of a weapon of mass destruction. He has been serving his sentence in a high-security supermax prison in Colorado.

Since December, the federal appeals court has been weighing if Tsarnaev had received a fair trial in Boston. 

His lawyers asked why the two jurors had not been dismissed, or at least why the trial judge had not asked them follow-up questions after the posts came to light on the eve of the trial.

The judges noted that the Boston court has a longstanding rule obligating such an inquiry.

Tsarnaev's lawyers say one of the jurors, who would go one to become the jury's foreperson, or chief spokesperson, published two dozen tweets in the wake of the bombings. One post after Tsarnaev's capture called him a "piece of garbage."

Information from The Associated Press was used in this report.