The focus now isn’t on Dzhokhar Tsarnaev. It’s on the judge, the attorneys, and the jurors

This April 2015 courtroom sketch depicts US District Judge George O'Toole speaking during the sentencing phase of Dzkohkar Tsarnaev’s trial.REUTERS/File/Jane Collins/Reuters/file

For the first time in the Boston Marathon bombing case, all eyes won’t be on the perpetrator — and the odds may be tilting his way.

More than four years after Dzhokhar Tsarnaev, now 26, was convicted and sentenced to death for his role in the city’s worst terrorist attack, the proceeding has shifted to the federal appeals court in Boston. The focus will now be on the conduct of prosecutors, defense attorneys, the presiding judge — even the jury — with one central question at issue: Did Tsarnaev get a fair trial?

Oral arguments before three judges of the US Court of Appeals for the First Circuit are slated for Thursday. Tsarnaev is not expected to attend. Instead, lawyers are set to joust for two hours over legal questions such as whether the trial should have been held in Boston, and whether jurors failed to reveal their anti-Tsarnaev biases to the judge.

Defense attorneys will also argue that trial Judge George A. O’Toole Jr. erroneously withheld evidence from jurors that Tsarnaev’s older brother and accomplice, Tamerlan, had brutally killed three people two years earlier — a point that could have bolstered their argument that Tamerlan was the mastermind of the bombing and, had he lived to be tried, the only one deserving of a death sentence.

For the first time since the younger Tsarnaev was found hiding in a boat after a four-day manhunt in 2013, legal analysts said, the trend line in the case is leaning in his favor — a pattern that could force the trauma of a trial once again.

“There were very big risks in keeping the case in Boston — that’s why you have this extraordinary set of circumstances,” said George Kendall, a New York-based lawyer who specializes in death penalty cases and followed the trial in Boston. He said it was clear from the outset that it would be difficult to empanel an impartial jury in the same city where the bombs went off, at one of the city’s most cherished sporting events.

“Everyone knew that once you decided to keep the case in Boston, you really had to go the full mile to make sure any possible contaminating influences were really rooted out and put on the table,” he said. “But what you had here is jurors basically hiding stuff.”

If Tsarnaev’s case is overturned, prosecutors would have to decide whether to seek a death sentence again in a new trial or let him plead guilty and accept a life sentence (he has already admitted to the bombing).

It could take years for Tsarnaev to exhaust all of his appeals, but Thursday’s hearing provides the first outside review of the handling of the case.

“The definition of justice is providing a defendant a fair trial,” said Robert Dunham of the Death Penalty Information Center, which researches capital cases across the country. “People can disagree about what that means, but what it doesn’t mean is expediting an execution for the purpose of carrying out an execution without regard for the law.”

Nationwide, only one in six death sentences actually proceeds to an execution, and more than half of all death sentences are handed out in only three states: Texas, Virginia, and Missouri.

Massachusetts does not have the death penalty, but Tsarnaev was charged with crimes in the federal court system, which allows for capital punishment. And in the federal system, death sentences that actually result in executions are extremely rare: Since modern death penalty laws went into effect in 1988, only 82 people have been sentenced to death, and only three were actually executed — all before 2003.

No one has been executed for a crime in Massachusetts under modern death penalty laws, and the only other person sentenced to death in Massachusetts — admitted serial killer Gary Lee Sampson — is also appealing his sentence. The last time the state executed someone was in the 1940s.

Polls show most Massachusetts residents oppose the death penalty. In Tsarnaev’s case, the three members of the federal appeals court panel will explore how the jury was picked, how the jury reached a verdict for death, and how the judge’s decisions impacted the trial.

“What’s at stake is, did he get a fair trial? Or were the judge’s rulings so problematic . . . that you can’t trust the outcome of the trial,” said Albert “Buzz” Scherr, a University of New Hampshire law professor who has extensively researched death penalty issues.

“The context here is important; in capital cases, [the parties in the case] want to be really careful,” he added. “Everyone involved in the case, the prosecutors, defense lawyers, even the judge, are subconsciously saying, ‘Let’s be careful here, because of the potential consequence of making a mistake in what we’re deciding.’ ”

In legal filings over the last year, Tsarnaev’s lawyers argued that the trial should never have been held in Boston.

Before the trial got underway, O’Toole rejected the argument, saying he had set up a screening process that would filter out any juror bias.

But defense lawyers pointed to discoveries during the course of the trial that jurors may have withheld information about their past knowledge of the case: The foreperson, for instance, “hid 22 Twitter posts in which she had mourned the victims, praised police officers who would testify at trial, and called Tsarnaev a ‘piece of garbage,’ ” according to court records.

A second juror, according to court records, “started a Facebook discussion about the jury selection process, during which a friend urged him to ‘play the part,’ ‘get on the jury,’ and ‘send’ Tsarnaev ‘to jail where he will be taken care
of.’ ”

Prosecutors have argued in court records that the actual circumstances of the social media posts do not show the jurors were biased, and O’Toole downplayed them at the time. Before the jury was empaneled, he rejected a defense request to disqualify the jurors, saying that the arguments were “speculative,” and that the social media posts do not “suggest a bias that would be harmful to jury impartiality in this case.”

Defense attorneys argued that the effort to screen out juror bias proved to be “hollow,” and that the jurors’ failure to disclose their familiarity with the case showed it was impossible to pick a fair panel of jurors in Boston. They pointed to an appeals court decision in a separate case that came after Tsarnaev’s trial. The ruling, which came out of a federal court in Puerto Rico and would guide the appeals court deliberations in Boston, found that pretrial publicity about a case could be enough to taint a jury pool. In certain circumstances, the appeals court ruling found, such publicity should force the relocation of a trial to a new venue.

Tsarnaev’s lawyers wrote that the questions about the jurors’ preexisting prejudice against the defendant contributed to a “fundamentally unfair proceeding that damages the credibility of the American judicial system.”

“That dereliction of the unflagging duty to investigate colorable or plausible claims of juror misconduct would have been error in any trial. In a capital prosecution, it was intolerable,” the lawyers argued.

Tsarnaev, a son of Chechen immigrants who was raised in Cambridge, was convicted in 2015 of 30 counts related to the Marathon bombing, which killed three people: Lingzi Lu, a 23-year-old Boston University graduate student from China; Krystle Campbell, 29, of Arlington; and Martin Richard, an 8-year-old from Dorchester.

More than 260 other people were injured, including 17 who lost limbs, and Tsarnaev was also found responsible for the killing days after the blast of MIT police officer Sean Collier. Tamerlan Tsarnaev died during a firefight with police in Watertown that left a Transit police officer gravely wounded.

Of Dzhokhar Tsarnaev’s convictions, 17 counts allowed for capital punishment, and a federal jury agreed to sentence him to death specifically for the bomb that was in a backpack he placed in front of the Forum restaurant on Boylston Street; Richard and Lu were killed by that blast.

He became the first terrorist condemned to death by a jury in the United States in the post-9/11 world.

Soon we will learn whether he will keep that distinction — and whether the people of Boston, particularly the surviving victims of the bombing, will have to reexperience the trauma of his trial.