On Thursday, lawyers representing convicted 26-year-old Boston Marathon bomber, Dzhokhar Tsarnaev, will go before a three-judge panel of the U.S. Court of Appeals to argue that their client did not receive a fair trial in 2015. They will also ask that the death penalty in the case be rescinded.

Tsarnaev's legal team will argue that their client received neither a fair nor impartial trial and sentencing. The court is being asked to consider whether Judge George O'Toole acted properly, whether the nondisclosure of social media postings compromised jury selection and whether the death penalty decision was influenced by juror bias.

U.S. prosecutors, on the other hand, argue that Tsarnaev demonstrated callous disregard for the bombings' victims. In 2015 the defendant was charged with 30 counts, of which 17 were punishable by death.

Prior to the start of the 2015 trial, Tsarnaev's attorneys requested a change of venue, which O'Toole rejected. Tsarnaev's legal team now argues that O'Toole should not have allowed the trial to be held in Boston, since the city was widely viewed as a "victim" in the attack.

Robert Bloom, a law professor at Boston College specializing in criminal procedures, says high-profile trials are often moved to other venues for good reasons. He said finding an impartial jury in prominent cases where the crime occurred is difficult. The Tsarnaev case — which he compared to the Oklahoma City bombing in terms of its widespread impact on the local community — should not have been an exception.

"In Oklahoma there were many more people killed, but there are similarities," Bloom said. "The Timothy McVeigh trial was moved to Colorado. It was a U.S. district court judge who decided on venue, and venue is a kind of discretionary thing. On the other hand, O'Toole tried very hard to keep it in Boston and succeeded."

O'Toole's former colleague on the federal bench, Nancy Gertner, now a professor at Harvard Law School, said that keeping the case in Boston complicated the task of impaneling an impartial jury.

"Boston was the victim and not just conceptually, but also everyone was victimized by the lockdown that was ordered as police searched for the bombing suspects," Gertner said. "So there was a substantial question about whether the case should have been brought in Boston and a substantial question about timing."

The trial took place in spring 2015, around the time of the second anniversary of the bombing.

Gertner said that when a court rejects a change of venue, "one premise of that is that you will make sure that this is an extraordinarily careful voir dire."

But in this case, voir dire — the preliminary questioning of prospective jurors — was anything but careful, she said.

"Instead of asking the specific question about what people knew about the case," Gertner said, "[O'Toole] asked the most general, 'Have you heard about this case?' kind of question."

The defense also contends that jury selection was tainted by anti-Tsarnaev bias that was hidden from the judge.

Prior to the trial, O'Toole promised that he had put together a screening process that would filter out any juror bias.

But during the trial, two jurors, including the jury foreperson, failed to disclose a flurry of social media postings they had exchanged with friends about the case. The jury foreperson, according to the defense, described Tsarnaev on Twitter as "a piece of garbage" and also failed to mention that she had sheltered in place during the 18-hour search for the suspects on April 18, 2013. Court documents show that she was silent during voir dire about "22 Twitter posts in which she had mourned the victims" and praised police officers.

The court documents also revealed that a second juror exchanged messages on Facebook about the jury selection process. In one exchange a friend encouraged him to "'get on the jury,' and "send [Tsarnaev] to jail where he will be taken care of."

Gertner is incredulous that O'Toole did not replace the jurors when their social media postings were discovered.

"This was a singularly extraordinary thing to have happened in any case, but especially a death penalty case. When you have a juror who lied in answer to a question, in my view, that would have been enough to tip any verdict, at any time," she said.

But federal prosecutors rejected the argument that the postings rendered the jurors incapable of making unbiased decisions. O'Toole declined to disqualify them before the jury was empaneled and described the defense allegations that the jurors were biased as "speculative."

Tracey Maclin, a professor at Boston University specializing in constitutional law and criminal law and procedure, agrees with this view.

“I'm not surprised that people have social media comments and have received messages for a high-profile case," Maclin said. "Potential jurors are going to come to a trial certainly with some opinions. What's important is whether Judge O'Toole asked enough questions and determined that these jurors could put aside whatever initial views they had and decide the case neutrally.”

Tsarnaev's trial began on March 4, 2015 with Judith Clarke, the chief defense counsel, admitting that in a scheme with his older brother Tamerlan, her client set off one of the bombs near the Boston Marathon finish line two years earlier. For the defense what was mainly at stake was the penalty. Maclin thinks the defense will have a hard time convincing the court to overturn Tsarnaev's death sentence.

"Assuming that voir dire did not constitute a constitutional violation of ... the Sixth Amendment right to have a fair jury trial case,” the facts of the case justified the harshest of sentences, Maclin said. “When they put that bomb behind the family and the little boy was killed, if we're simply asking as a general matter, 'Do these facts, do these crimes justify imposing a death penalty?' My answer would be yes. “

But the defense will try to convince the court otherwise. During the original trial, Tsarnaev’s lawyers tried to introduce what they called mitigating evidence to show that he was under the control of his older brother Tamerlan, who was killed in a shootout in Watertown with police four days after the marathon. Recently unsealed documents indicate that Tamerlan took part in a grisly triple homicide in Waltham approximately 18 months before the bombing. Tsarnaev's legal team will tell the three-judge appellate panel that if O'Toole had allowed these documents into the court record it would have shown that the defendant was under the influence of his murderous brother.

The bombings took the lives of 8-year-old Martin Richard from Dorchester, Mass., 23-year-old Lingzi Lu, a Boston University graduate student from China, and 29-year-old Krystle Campbell from Arlington, Mass. Also killed was an MIT police officer, Sean Collier, who was shot by the Tsarnaevs as he sat in his cruiser on the university campus.

The appeals court is not expected to rule right away.