A man prays at a makeshift memorial outside the Tree of Life synagogue in Pittsburgh, Pennsylvania, Oct. 31, 2018. Photo: Reuters / Cathal McNaughton.

The man accused of a Pittsburgh synagogue shooting rampage that killed 11 people during Sabbath prayers was due to be arraigned in federal court on Monday, charged with dozens of offenses including murder and hate crimes.

Robert Bowers, who had frequently posted antisemitic slurs and conspiracy theories online, is accused of bursting into the Tree of Life synagogue on Oct. 27 armed with three handguns and a semi-automatic rifle, then firing on congregants as he shouted, “All Jews must die.” The shooting in the heart of the city’s heavily Jewish Squirrel Hill neighborhood marked the deadliest antisemitic attack in US history.

Bowers, a 46-year-old former truck driver, could face the death penalty if convicted.

He pleaded not guilty in November to 44 initial counts, including using a firearm to commit murder and obstruction of religious exercise resulting in death. On Jan. 29, a federal grand jury indicted Bowers on 19 additional charges, including hate crime violations.

Among those killed were a 97-year-old woman, two brothers in their 50s and a married couple in their 80s. Two civilians and five police officers were wounded before the suspect was shot by police and surrendered.

On the day of the attack, Bowers, a Pittsburgh resident, said online, “I can’t sit by and watch my people get slaughtered. Screw your optics, I’m going in.”

The attack followed a wave of politically motivated pipe bombs mailed to prominent Democrats and heightened national tensions ahead of November’s midterm congressional elections.

It also fueled a national debate over the rhetoric of US President Donald Trump, who critics say contributed to a surge in white nationalist and neo-Nazi activity. The Trump administration has rejected the notion he has encouraged far-right extremists who have embraced him.