Bowers was hospitalized in fair condition with multiple gunshot wounds, authorities said.
It wasn't clear whether Bowers had an attorney to speak on his behalf.
Saturday's attack came at a time of heightened tensions - a day after a Trump supporter from Florida was arrested for mailing explosive devices to Democrats and liberals, setting the country on edge ahead of close-fought elections on Nov 6.
Bowers' alleged attack on innocent worshipers in Pittsburgh was an evil, irrational and unjustified act of savagery motivated by hatred against Jews, and part of an unmistakable trend of growing anti-Semitism in the U.S., Canada and around the world.
Robert Jones, special agent for FBI Pittsburgh division, said there could have been further violence if Bowers had made it out of the synagogue. It appears Bowers acted alone, authorities said.
People listen to interfaith speakers at the Soldiers and Sailors Memorial Hall during a service to honor and mourn the victims of Saturday's mass shooting at the Tree Of Life Synagogue on October 28, 2018 in Pittsburgh, Pennsylvania. "He gets up in the morning with new and inventive ways to divide us", Schiff said on CNN's State of the Union.
Bowers will make his first court appearance at 1.30pm on Monday at the Joseph F. Weis, Jr.
"Please fill our synagogues this Saturday", Shaken said. Authorities in New York City, Chicago and elsewhere increased security at Jewish centers.
A social media post by synagogue shooting suspect Robert Bowers. Almost 20 posts used the n-word.
Other posts referenced false conspiracy theories suggesting the Holocaust - in which an estimated 6 million Jews perished - was a hoax.
Using a slur for Jews, he said, "There is no #MAGA, as long as there is a k-- infestation".
He added that Canada is not immune to this type of tragedy and hatred, pointing to the mass shooting at a Quebec City mosque early previous year that killed six people. I can't wait while my people are getting slaughtered. "Screw your optics, I'm going in". The organization says it is guided by Jewish values and history. The Anti-Defamation League called it the deadliest USA attack on Jews.
"I said, 'Oh, I'm Jewish, too.' It kind of started the friendship", DeFelice told The Pittsburgh Post-Gazette.
Gab said on Twitter that it was "under attack".
"The entire people of Israel grieve with the families of the dead", Netanyahu said.
Similar events took place nationwide, with words of solace pouring in from the US Jewish community - the largest outside Israel - as well as the pope and European leaders. "We all pray for the speedy recovery of the wounded". One has been discharged, one is due to be, and the other two "need more doing to them" Pennsylvania police confirmed. A chant of "vote, vote, vote" broke out during the emotional gathering.
More than half a century ago, when four young girls were killed in a Birmingham church by a racist's bomb, Dr. King told us that those little girls "have something to say to every politician who has fed his constituents with the stale bread of hatred and the spoiled meat of racism...."
Cecil Rosenthal, 59, and David Rosenthal, 54, were intellectually disabled and lived together near the synagogue. Among its treasures is a "Holocaust Torah", rescued from Czechoslovakia.
My family is from Pittsburgh and I've sat in Tree of Life many times before. "When American citizens can not freely and safely worship in their house of worship and celebrate the Sabbath, it concerns me because it challenges the safety and security of all Americans in any house of worship".
Said Stephen Cohen, co-president of New Light Congregation: "The loss is incalculable".
Snider had just been released from a six-week hospital stay for pneumonia and was not at Saturday's services.