The federal trial of a 50-year-old truck driver convicted of killing 11 people at a Pittsburgh synagogue in the deadliest antisemitic attack in U.S. history is in its third and final phase, in which jurors must decide whether to sentence him to death.

The jury convicted Robert Bowers in June after three weeks of testimony about how he stormed the Tree of Life synagogue in October 2018 and shot anyone he saw. He killed members of three congregations that were sharing the building, and wounded two worshippers and five police officers.

During the second phase of the trial, it took jurors only two hours to decide that Bowers was legally eligible for the death penalty. That led to the final phase, which is more emotionally taxing for jurors as they weigh whether sentence the man across the courtroom to die.

Here is a look at the final phase:

IS THERE ANY WAY TO PREDICT THE OUTCOME?

Given the overwhelming evidence, everyone including Bowers’ lawyers knew a conviction was all but certain.

The outcome of sentencing phases are notoriously unpredictable, though, because it only takes one holdout juror to prevent the unanimity required for a death sentence. Without it, a defendant automatically gets life in prison without the possibility of parole.

Jury selection is designed, among other things, to weed out those who say they could never sentence someone to die. But it’s not uncommon in such cases for juries to deadlock.

It happened at a federal capital trial this year for Sayfullo Saipov, who was convicted of killing eight people in 2017 by running them down with truck along a New York City bike path. A split among jurors meant Saipov got a life term.

If Bowers gets a death sentence, it would be a first at a federal trial during the presidency of Joe Biden, the first U.S. president to have opposed capital punishment prior to taking office. It would also be years before he would be executed, given appeals and a current moratorium on federal executions.

The most recent federal executions — there were 13 in the final months of Donald Trump’s presidency — were carried out by lethal injections of pentobarbital at an Indiana prison where federal death row is located.

WHY THIS FINAL STAGE?

This stage is meant to let jurors closely scrutinize Bowers to determine if he is truly the worst of the worst and therefore deserving of the death penalty.

During the sentencing stage, prosecutors and the defense are given more leeway to discuss Bowers’ wider life, much of which would have been ruled inadmissible earlier.

Most federal capital trials combine the eligibility and sentencing decisions in a second, final stage. But courts have discretion over whether to divide up the process.

WHICH SIDE FACES THE HEAVIER BURDEN?

Higher courts have said the presumption is that defendants should get life in prison, according to guides for death penalty lawyers on the Federal Death Penalty Resource Counsel website.

That puts the burden on the prosecution to prove Bowers’ actions were so depraved and his character so irredeemable that a death sentence is warranted.

Prosecutors must prove beyond a reasonable doubt that aggravating factors counting in favor of Bowers’ execution outweigh any mitigating factors that might call for a life sentence.

WHAT ARE SOME AGGRAVATING FACTORS IN THE SYNAGOGUE SHOOTING?

The prosecution told jurors at the outset of the sentencing phase that Bowers killed people who were uniquely vulnerable, including a woman in her 90s and three people in their 80s.

“These were not victims who could run away or fight back. They were easy prey,” prosecutor Nicole Vasquez Schmitt said Monday.

Prosecutors have also emphasized that Bowers carefully planned the massacre. And they have been highlighting his antisemitism throughout the trial.

“He hated Jews and wanted to kill as many as he could,” Vasquez Schmitt told jurors this week.

WHAT ABOUT MITIGATING FACTORS?

Bowers’ lawyers have repeatedly argued that serious mental disorders and profound childhood traumas make him less culpable for the synagogue attack.

His attorney Elisa Long told jurors Monday that Bowers’ father took his own life after being charged with rape and that when Bowers was a child, his mother told him she wished he’d never been born.

Proving a defendant showed remorse is usually a critical mitigating factor. But that will be difficult in this case, given statements prosecutors say Bowers made to mental health analysts while in jail, including that he repeated antisemitic stereotypes and said he regretted not killing more Jews.

WHAT ABOUT THE VERDICT FORMS?

Verdict forms usually list all of the potential aggravating and mitigating factors. They can be lengthy. The one in Saipov’s case was 18 pages long.

The mitigating factors Saipov’s jurors accepted included that he wasn’t a leader of the terrorist group he expressed allegiance to and that he had family who condemned his actions but still loved him.

Among the aggravating factors they accepted was that he sought to terrorize the community.

HOW DOES THE JURY BALANCE THE FACTORS?

Jurors must be unanimous in accepting any aggravating factor using the high reasonable-doubt standard. A mitigating factor can be considered even if only one juror accepts it.

The U.S. Supreme Court has said jurors must unanimously find at least one aggravating factor before they can impose the death penalty. But they can find no mitigating factors and still opt for a life sentence.

In weighing all factors in deliberations, courts have instructed jurors not to decide the sentence simply based on whether there are more aggravating or mitigating factors. Ultimately, the weight jurors give to different factors is subjective.

WHAT ABOUT SURVIVORS AND VICTIMS’ RELATIVES?

Jurors have been hearing from them about the trauma Bowers inflicted.

On Monday, survivor Carol Black testified about her brother, 65-year-old Richard Gottfried, a dentist Bowers killed.

“It’s just such a huge void in our family, for him not to be here,” she said.

There are restrictions on what victims and relatives can say. Judges usually bar them from telling jurors they want defendants to die for their crimes.

Defense lawyers often have their client’s family members testify to try and persuade jurors that a defendant isn’t all bad, including by singling out some past act of kindness.

WHAT ARE SOME OTHER CONSIDERATIONS?

One could be the danger Bowers might pose if he goes to prison for life. Prosecutors often argue that even behind bars, a defendant could kill again, be it a fellow inmate or guard.

Defense attorneys sometimes seek to enter statistics that show those imprisoned for violent crimes aren’t necessarily prone to violence behind bars. Research on that point is inconclusive.

(AP)