PITTSBURGH (Reuters) – The names of those shot dead by a gunman yelling “All Jews must die” will be released on Sunday after the deadliest attack on the Jewish community in the United States, officials said.

People mourn the loss of life as they hold a vigil for the victims of Pittsburgh synagogue shooting in Pittsburgh, Pennsylvania, U.S., October 27, 2018. REUTERS/John Altdorfer

The gunman stormed a Pittsburgh synagogue during Saturday services, killing 11 worshippers and wounding six other people including four police officers, before he was arrested.

Pittsburg Mayor Bill Peduto told CBS television station KDKA that when the list of the dead is released by federal officials at a news conference at 9 a.m. on Sunday, it “will rip your heart out”, saying he personally knew some of the victims.

The Tree of Life synagogue in the city’s Squirrel Hill neighborhood, a heavily Jewish area, was holding a Shabbat religious service at the time of the shooting.

The mass shooting prompted security alerts at houses of worship around the country. It follows a spate of pipe bombs found mailed in recent days to prominent political figures, mostly Democrats including former President Barack Obama.

The U.S. Attorney’s Office said it would make public the charging complaint and an official affidavit, which may shed light on why Robert Bowers, 46, of Pittsburgh, allegedly shot the worshippers.

Bowers had made many anti-Semitic posts online, including one early on Saturday. In another, he slammed U.S. President Donald Trump for doing nothing to stop an “infestation” of the United States by Jews.

A social media post by Bowers on Saturday morning said a Jewish refugee organization, the Hebrew Immigrant Aid Society, “likes to bring invaders in that kill our people. I can’t sit by and watch my people get slaughtered. Screw your optics, I’m going in”.

The comment was posted on Gab, a Philadelphia, Pennsylvania-based social networking service created as an alternative to Twitter. In a statement, Gab.com confirmed the profile belonged to Bowers and also said it had suspended the account and contacted the FBI about it.

Bowers was taken into custody after a shootout with a SWAT team. Federal prosecutors charged him with 29 criminal counts including violence and firearms offenses, and violating U.S. civil rights laws.

“The actions of Robert Bowers represent the worst of humanity. We are dedicating the entire resources of my office to this federal hate crime investigation and prosecution,” U.S. attorney for western Pennsylvania Scott Brady told reporters.

U.S. Attorney General Jeff Sessions said federal prosecutors could seek the death penalty.