(Reuters) -The man accused of killing 11 worshippers at a Pittsburgh synagogue five years ago in the deadliest antisemitic attack in U.S. history could face the death penalty if found guilty in a federal trial that opened on Tuesday.

Robert Bowers, 50, is standing trial on dozens of federal charges including 11 counts of hate crimes resulting in death in the mass shooting at Pittsburgh’s Tree of Life synagogue on Oct. 27, 2018. He has pleaded not guilty.

On Tuesday, Judy Clarke, a defense lawyer for Bowers, told jurors in an opening statement that there was no dispute that he carried out the attack, calling him “a socially awkward man who didn’t have many friends,” the Pittsburgh Post-Gazette reported. She acknowledged that Bowers posted violent antisemitic messages on a right-wing website and lamented the “loss and devastation” her client caused.

Still, Clarke indicated that prosecutors would not be able to cross the high bar required to convict him on the most serious capital charges and to sentence him to death.

“These are federal charges, not straightforward murder charges,” she said, according to the Gazette, and referred to Bowers’ “misguided intent” and “irrational thoughts.”

The trial in U.S. District Court in Pittsburgh in western Pennsylvania is expected to take weeks to complete. If the jury finds Bowers guilty of capital offenses in the first phase of the trial, they will then determine whether he spends the rest of his life in prison or is executed by lethal injection. All 12 jurors must vote unanimously in order to sentence Bowers to death.

In seeking the death penalty, federal prosecutors will try to show that aggravating factors were involved, making a case that Bowers carefully planned the attack and that he targeted vulnerable victims. Most of the victims were elderly.

“The defendant had moved methodically through the synagogue to find the Jews he hated and kill them,” Soo C. Song, an assistant U.S. attorney, told jurors in the prosecution’s opening remarks, the Gazette reported.

In court filings, lawyers for Bowers have repeatedly tried to get the court to rule out the death penalty as a sentencing option, calling it unconstitutional on the grounds that he suffers from major mental illness including schizophrenia.

A one-time truck driver who frequently posted antisemitic slurs online, Bowers stormed the synagogue during Saturday services and yelled, “All Jews must die,” according to prosecutors.

In addition to the deceased, two other worshippers were wounded along with five police officers. Bowers surrendered and was taken into custody after he was wounded in a shootout with police.

Bowers was carrying multiple guns when he entered the synagogue in the city’s Squirrel Hill neighborhood, where many residents are Jewish, federal authorities have said.

U.S. Attorney General Merrick Garland has ordered a moratorium on executions while the U.S. Department of Justice reviews its death penalty protocols.

(Reporting by Brendan O’Brien in Chicago; Additional reporting by Jonathan Allen; Editing by Conor Humphries and Cynthia Osterman)

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