Stephen Weiss, a 60-year-old member of the congregation, described hearing dozens of shots coming from the synagogue’s front lobby.
“We had services going on in the chapel when we heard a loud noise,” he told the Tribune-Review newspaper. “I recognized it as gunshots.”
Authorities said Bowers was armed with an assault rifle and at least three handguns when he opened fire shortly before 10:00 am (1400 GMT) – leaving a scene described as “horrific” by Wendell Hissrich, Pittsburgh’s public safety director.
“One of the worst that I’ve seen. I’ve been on plane crashes,” said Hissrich, who confirmed that 11 people were killed, and six injured. No children were among the casualties.
“It’s sickening. Outside of just the evil factor of it, who wakes up on a Saturday morning to do that?” said Pittsburgh chef Nathan, 42, who came to pay his respects but refused to give his second name.
“Hate Has No Home Here,” read a placard in a simple memorial, next to a heart-shaped US flag – the same slogan repeated in Hebrew and Arabic, with candles and bouquets of pink roses and carnations.
The United States is witnessing a sharp spike in anti-Semitic incidents, surging 57 percent from 2016 to 2017, to 1,986 from 1,267, according to the Anti-Defamation League, a civil rights group which has tracked anti-Semitism in the United States since the 1970s.
The ADL said it believes the Pittsburgh shooting to be the deadliest such attack in US history.
“Our hearts break for the victims, their families, and the entire Jewish community,” said the group’s head Jonathan Greenblatt.
Bowers, who the FBI said was not previously known to law enforcement, appeared to be the author of a rash of anti-Semitic online posts, notably on the Gab.com website, where conspiracy theories are common.