death penalty. In another, he slammed President Donald Trump for doing nothing to stop an "infestation" of the United States by Jews.
"This evil anti-Semitic attack is an assault on all of us", Trump told supporters at an election rally in IL where he drew loud cheers as he vowed to fully enforce the death penalty for such crimes.
US President Trump ordered flags to be flown at half-staff in "solemn respect" for the shooting victims.
Stephen Weiss, a 60-year-old member of the congregation, described hearing dozens of shots coming from the synagogue's front lobby. "We're not going to be deterred", Barkley tells TIME. "I recognised it as gunshots".
"It's one of the worst that I've seen and I've been on some plane crashes", said a visibly moved Wendell Hissrich, the Pittsburgh public safety director.
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".
The number of anti-Semitic incidents in the United States rose 57 percent in 2017, according to a report by Jewish civil rights group the Anti-Defamation League (ADL) released earlier this year.
Canadian Prime Minister Justin Trudeau took to Twitter, writing, "Canadians' hearts are with the Jewish community in Pittsburgh today, as they endured a horrific anti-Semitic attack while at prayer".
Law enforcement officials told CNN Bowers' social media postings had targeted Jews.
On social media cite Gab, a Facebook-like platform popular with right-wing extremists and conservatives, he said "Jews are the children of Satan", and had used well known Neo-Nazi symbols and codes on his background photos, according to news reports, His account was taken down by the site later.
With both the death toll and details of the synagogue's security still to be disclosed, Trump said gun control "has little to do with it" but "if they had protection inside, the results would have been far better".
Mr Trump - who has been accused of fueling hate with divisive rhetoric - briefly considered scrapping his IL campaign rally on Saturday, but finally made a decision to maintain it. "So they do not lock the door, and anybody can just walk in", said Marilyn Honigsberg, administrative assistant for New Light.
In a statement, Gab.com confirmed the profile belonged to Bowers and also said it had suspended the account and contacted the Federal Bureau of Investigation about it.
German Chancellor Angela Merkel slammed an act of "blind anti-Semitic hatred", saying: "We all have to stand up against anti-Semitism, everywhere".
"Canadian Muslims stand with firm resolve against anti-Semitism, religious bigotry, xenophobia and hate". The tree-lined residential neighborhood of Squirrel Hill, about 10 minutes from downtown Pittsburgh, is the hub of Pittsburgh's Jewish community.
While Trump has claimed he is the "least anti-Semitic" person around, he has been accused of not forcefully speaking against the rising wave of anti-Semitism.