A mass murderer who is accused of murdering 11 people at the Tree of Life synagogue considered Jews to be a “cancer upon the planet” and hunted down his victims as they hid in the pews, a federal prosecutor said in court.

Robert Bowers' federal trial got underway more than four years after the shooting deaths of 11 worshippers at the Tree of Life synagogue in Pittsburgh.

Twelve jurors and six alternates, which include 11 women and seven men are hearing the case.

Bowers, who could face the death penalty if convicted of some of the 63 counts he faced for the October 2018 attack, showed no reaction during the prosection opening statement on Tuesday, May 30. 

The attack claimed the lives of worshippers from three congregations who were sharing the building, Dor Hadash, New Light and Tree of Life. 

The court heard how Bowers carefully planned the shooting using multiple weapons and boasted of his intent on social media moments before he entered the synagogue in Pittsburgh’s Squirrel Hill neighbourhood.

pittsburgh shooter Robert Bowers

Robert Bowers (Photo: Butler County Prison)

Assistant U.S. Attorney Soo C. Song added in her opening statement: “The depths of the defendant's malice and hate can only be proven in the broken bodies" of the victims and "his hateful words.”

Song said after officers apprehended Bowers and asked why he did it, he blurted out: "All Jews need to die, Jews are killing our kids, Jews are bringing immigrants and killing our people and committing genocide and Jews are the children of Satan."

Charges include 11 counts each of obstruction of free exercise of religion resulting in death and hate crimes resulting in death.

Members of the three congregations arrived at Pittsburgh courthouse in a school bus and entered together. 

Bowers, a truck driver from the Pittsburgh suburb of Baldwin, had offered to plead guilty in return for a life sentence however US federal prosecutors turned him down and are pursuing the death penalty. Bowers' lawyers also recently said he has schizophrenia and brain impairments.

Prosecutors are expected to tell jurors about incriminatory statements Bowers allegedly made to investigators, an online trail of antisemitic statements that they say shows the attack was motivated by religious hatred, and the guns recovered from him at the crime scene, where police shot Bowers three times before he surrendered.

They indicated in court filings that they might introduce autopsy records and 911 recordings during the trial, including recordings of two calls from victims who were subsequently shot to death.