Police confirmed the suspect Robert Bowers was in custody after he walked into the building and yelled “all Jews must die” before opening fire.
All 11 victims of the synagogue shooting in Pittsburgh have been identified and their families notified, US authorities said on Sunday.
“After difficult work by the medical examiner’s office, all 11 victims were positively identified and next of kin notifications took place,” Robert Jones, the FBI agent in charge of the investigation, said at an early-morning press briefing.
They ranged in age from 54 to 97, said Karl Williams, the county medical examiner. They included two brothers and one married couple.
A gunman yelling “all Jews must die” stormed a Pittsburgh synagogue during Saturday services and shot worshippers, killing at least 11 and wounding six including four police officers before he was arrested.
Police have identified the suspect as Robert Bowers, 46, of Pittsburgh, who is now in custody.
Federal prosecutors say Bowers was charged on Saturday night in a 29-count criminal complaint, including obstructing the exercise of religious beliefs resulting in death.
The charges also include 11 counts of using a firearm to commit murder, weapons offences and charges alleging Bowers seriously injured police officers. It wasn't immediately known if he has an attorney.
A social media post on Gab.com by with a user of the same name earlier in the day said a Jewish refugee organisation, the Hebrew Immigrant Aid Society (HAIS), "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.”
HIAS is a Maryland-based nonprofit group that helps refugees around the world. The organisation says it is guided by Jewish values and history. President and CEO of the group Mark Hetfield said he wasn't aware of the shooter's "obsession with HIAS until this morning."
TRT World's Christine Pirovolakis reports.
In a statement, Gab.com - a Philadelphia, Pennsylvania-based social networking service created as an alternative to Twitter - confirmed the profile belonged to Bowers.
"Gab took swift and proactive action to contact law enforcement immediately," it said. "We first backed up all user data from the account and then proceeded to suspend the account. We then contacted the FBI and made them aware of this account and the user data in our possession."
Three police officers were shot and one was injured by shrapnel, Alleghany County spokeswoman Amie Downs said in an email. Two of the six people injured were in critical condition, Downs said, but would not immediately say if the count of six injured people included the suspect.
"It's a very horrific crime scene, one of the worst that I've seen," Pittsburgh public safety director Wendell Hissrich told a news conference near the scene.
"This falls under hate crime," he said, adding there was no active threat to the community and that the shooter had been taken to a hospital.
The shooting, for which one federal law enforcement official said Bowers used an AR-15 assault-style rifle, triggered 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.
Police surrounded the Tree of Life synagogue in the city's Squirrel Hill neighbourhood, a heavily Jewish area. The synagogue was holding a Shabbat religious service at the time.
Police are normally only present at the synagogue for security on high holidays, Michael Eisenberg, former president of the synagogue, told US media.
"On a day like today, the door is open, it’s a religious service, you can walk in and out," he said.
Trump condemns attack
US President Donald Trump on Saturday said he will travel to Pittsburgh.
Trump - who is in Illinois for a campaign rally ahead of key November midterm elections - did not provide details of his trip that comes in the wake of the fatal shooting, which he earlier dubbed an "evil Anti-Semitic attack" and an "assault on humanity."
"All of America is in mourning over the mass murder of Jewish Americans," the Republican president tweeted.
All of America is in mourning over the mass murder of Jewish Americans at the Tree of Life Synagogue in Pittsburgh. We pray for those who perished and their loved ones, and our hearts go out to the brave police officers who sustained serious injuries...— Donald J. Trump (@realDonaldTrump) October 27, 2018
Earlier in the day Trump called the shooting "a wicked act of mass murder and pure evil" and called on Americans to rise above hate and move past divisions.
Trump said at the start of a campaign rally in Indianapolis that anti-Semitism "must be condemned and confronted everywhere and anywhere it appears."
Meanwhile, Turkish President Recep Tayyip Erdogan condemned the attack in a tweet which read, “I condemn the terror attack against a Pittsburgh synagogue and extend my heartfelt condolences to the families of the victims and to the American people. Turkey unequivocally condemns all forms of terrorism in all parts of the world regardless of their targets."
Jonathan Greenblatt, CEO of the Anti-Defemation League, called the shooting an "anti-Semitic attack." Israeli Prime Minister Benjamin Netanyahu said he was heartbroken, describing the attack as "horrendous anti-Semitic brutality."
Around the time of the shooting, three congregations amounting to more than 100 people would have been using the building, Eisenberg said. Most of the congregants were older people, according to a former rabbi interviewed by local media.
Shortly after reports of the shooting emerged, US President Donald Trump said in a tweet he was watching what he described as a "devastating" situation.
Earlier, Trump told reporters later that the killings might have been prevented if there had been an armed guard in the building.
“If they had some kind of a protection inside the temple maybe it could have been a much more different situation, they didn’t," he said when asked about a possible link to US gun laws.
Steve Irwin is an attorney who has attended the Tree of Life synagogue. He says current laws are not good enough to prevent mass shootings.