The worst atrocity against Jews in American history was committed with five minutes’ notice.

At 9.49am last Saturday, Robert Gregory Bowers wrote the chilling words “I’m going in” to conclude a social media post attacking a Jewish refugee charity.

A short time later the first 911 calls began to come from inside Pittsburgh’s Tree of Life synagogue, where Shabbat services were underway. The 46-year-old self-employed lorry driver had marched inside carrying an assault rifle and three handguns.

After a little over an hour, eleven people were dead. Mr Bowers, who was shot and wounded in a gun battle with police, is in custody as the only suspect.

He later repotedly told officers “I just want to kill Jews” and “all these Jews need to die”.

Among his victims were Cecil and David Rosenthal.

“They were two developmentally disabled brothers who never seemed to miss a single Shabbat service,” one long-term Tree of Life member, Elissa Wald, said. “Cecil was the greeter, warmly hailing everyone as they came in.”

Greeting was also a role taken on by another victim, Irving Younger, 69, a retired estate agent.

Many of those who perished were grandparents. They included Daniel Stein, 71, a president of the synagogue’s Men’s Club who doted on his grandson, and 87-year-old Melvin Wax, who was leading a Shabbat service in the basement when the gunman struck.

Dr Jerry Rabinowitz, 66, was, one of his patients reflected, “the one to go to” to fight HIV in Pittsburgh before effective treatment existed. 65-year-old Richard Gottfried, a dentist, was known for handing out toothbrushes rather than sweets to children on Halloween.

Toronto native Joyce Fienberg spent 25 years at the University of Pittsburgh developing ways to improve classroom teaching in schools.

The oldest victim, 97-year-old Rose Mallinger, was said to have barely missed a service in decades, while a 1956 article in the Pittsburgh Press records the marriage of Sylvan Simon to his new wife Bernice in a candlelit ceremony in the Tree of Life synagogue. They died together on Saturday in the same building, now aged 86 and 84, two months before their 62nd wedding anniversary.

The Jewish community of Pittsburgh dates back to the mid-19th century, when a small group of German Jews settled in the area. It is a typical American Jewish community — vibrant, stable, and relatively prosperous. Until recently its claim to fame was the 1885 Pittsburgh Platform, the controversial document that established the American Reform movement.

Since the 1920s, Jewish life in Pittsburgh has largely centered around Squirrel Hill, a neighbourhood of some twenty synagogues, numerous kosher restaurants and Jewish day schools.

Founded in the 1860s, the Conservative Tree of Life congregation is one of the oldest. Its building is an airy, spacious synagogue, with large stained glass windows, gardens, and a Torah scroll rescued from the Holocaust.

Before Saturday, Robert Bowers appeared to have been a law-abiding citizen with only a 2015 traffic violation to his name. He now faces 29 charges, including obstructing the exercise of religious beliefs resulting in death — a hate crime. Federal prosecutors indicated he could now face the death penalty.

President Donald Trump and his daughter Ivanka, who converted to Judaism, laid stones on the eleven memorials outside the Tree of Life synagogue and met the rabbi on Tuesday.

His spokeswoman later said it had been a “very humbling and sad” visit — but for many in the community, Mr Trump’s divisive policies had a role to play in the atrocity.

It was a view voiced by 4,000 demonstrators who gathered nearby in the synagogue’s Squirrel Hill neighbourhood, where a speaker told the crowd: “Your words and your policies have emboldened the white nationalist movement.”

On one placard, the message was even more stark: “Trump, apologise for stoking the hatred or go home!”