The three-judge panel of the 1st US Circuit Court of Appeals in Boston rendered the decision more than six months after arguments were heard in the case.
The April 15, 2013 attack killed three people and injured more than 260 others.
Tsarnaev’s lawyers argued that intense media coverage made a fair trial in Boston impossible. They also pointed to social media posts from two jurors suggesting they had strong opinions even before the 2015 trial began.
The appeal judges, during a hearing on the case in early December, devoted a significant number of questions to the jury’s bias argument.
They asked why the two jurors weren’t fired, or at least why the trial judge didn’t ask them follow-up questions after the positions were revealed on the eve of the trial.
The judges noted that the Boston court has a long-standing rule requiring such an investigation.
Tsarnaev’s lawyers say one of the jurors, who would make one to become the jury foreman, or chief spokesperson, posted two dozen tweets in the wake of the bombings. A message after Tsarnaev’s capture called it “garbage”.
Tsarnaev was found guilty on 30 counts, including conspiracy and use of a weapon of mass destruction. He is serving his sentence in a super-max high-security Colorado prison.
Her brother, Tamerlan Tsarnaev, was killed in a shootout with police days after the two brothers detonated two pressure cooker bombs near the marathon finish line.