PITTSBURGH (AP/WTXF) -- Tributes rolled in Sunday to the victims of the Pittsburgh synagogue massacre as authorities worked to piece together the background and movements of the suspected gunman, who authorities said expressed hatred of Jews as he opened fire with an AR-15 rifle and other weapons and later told police, "All these Jews need to die."
Robert Gregory Bowers killed eight men and three women inside the Tree of Life Synagogue on Saturday during worship services before a tactical police team tracked him down and shot him, authorities said in state and federal affidavits made public on Sunday.
Six people were injured in the attack, including four officers.
Officials released the names of all 11 of the dead, all of them middle-aged or elderly. The victims included intellectually disabled brothers and a husband and wife. The youngest was 54 and the oldest was 97.
"The loss is incalculable," said Stephen Cohen, co-president of New Light Congregation, which rents space at Tree of Life.
Mayor Bill Peduto called it the "darkest day of Pittsburgh's history."
Bowers shot his victims with an AR-15 -- the weapon used in many of the nation's mass shootings -- and three handguns, all of which he owned legally and had a license to carry, according to a law enforcement official who wasn't authorized to discuss the ongoing investigation, and spoke Sunday on condition of anonymity.
Little else was known about Bowers, who had no apparent criminal record but who is believed to have expressed virulently anti-Semitic views on social media. It appears he acted alone, authorities said.
His neighbor, Chris Hall, said he never heard or saw anything to indicate that Bowers harbored anti-Semitic views or posed a threat. Bowers kept to himself, he said.
"The most terrifying thing is just how normal he seemed," Hall said. "I wish I knew what was going on inside his head. Maybe something could have been done. I don't know."
The victims included Melvin Wax, a retired accountant in his late 80s who was always one of the first to arrive at synagogue and among the last to leave.
"He and I used to, at the end of services, try to tell a joke or two to each other," said Myron Snider, a fellow member of New Light Congregation, which rented space in the basement of Tree of Life. "Most of the time they were clean jokes. Most of the time. I won't say all the time. But most of the time."
The toll also included professors, dentists and physicians.
The University of Pittsburgh Medical Center tweeted it mourned the loss of Dr. Jerry Rabinowitz, 66, "one of the kindest physicians and human beings in our community."
Two other victims, Cecil Rosenthal, 59, and his younger brother David Rosenthal, 54, were intellectually disabled and lived together in Pittsburgh's Squirrel Hill neighborhood, near the synagogue where they were killed.
"Cecil's laugh was infectious. David was so kind and had such a gentle spirit. Together, they looked out for one another. They were inseparable," said Chris Schopf, vice president of residential supports for ACHIEVA, which helped the brothers live independently. "Most of all, they were kind, good people with a strong faith and respect for everyone around."
Vigils were planned in Pittsburgh, Washington and elsewhere, while the Pittsburgh Steelers and Cleveland Browns observed a moment of silence at Heinz Field on Sunday.
Bowers apparently posted an anti-Semitic message on a social media account linked to him just a few minutes before he opened fire during Sabbath services on Saturday morning. After the attack, he told an officer, "I just want to kill Jews," according to a federal affidavit.
The gunman targeted a building that housed three separate congregations, all of which were conducting Sabbath services when the attack began just before 10 a.m. in the tree-lined residential neighborhood of Squirrel Hill, about 10 minutes from downtown Pittsburgh and the hub of the city's Jewish community.
The Jewish community is "an important part of the cultural and social identity of Pittsburgh, and so this was an attack upon our neighbors and upon our friends," said Scott Brady, the chief federal prosecutor in western Pennsylvania.
Retired Tree of Life Rabbi Alvin Berkun, who knew nearly all of the victims, said Bowers penetrated all three areas of the synagogue where the worshippers were gathered. The synagogue pays police officers to provide security on high holidays, but not at other times, he said.
"When that was over, there's virtually no security," he said. "We were lax in our vigilance."
Michael Eisenberg, the immediate past president of the Tree of Life, said synagogue officials had not received any threats that he knew of before the shooting. But security was a concern, he said, and the synagogue had started working to improve it.
Cohen said leaders of New Light Congregation -- which rents space at Tree of Life -- had participated in active-shooting drills, "and I think that's what ultimately saved the people who were saved."
Cohen, who was not at the synagogue on Saturday, said the congregation -- which lost three of its members in the rampage -- meets in the basement of the building, which is partially protected by a steel door. The rabbi, Jonathan Perlman, shepherded some of the congregants behind the door "and actually saved them," Cohen said.
Bowers was charged with 11 state counts of criminal homicide, six counts of aggravated assault and 13 counts of ethnic intimidation in what the leader of the Anti-Defamation League called the deadliest attack on Jews in U.S. history.
He was also charged in a 29-count federal criminal complaint that included counts of obstructing the free exercise of religious beliefs resulting in death -- a federal hate crime -- and using a firearm to commit murder. U.S. Attorney General Jeff Sessions said the charges could merit a death sentence.
Bowers, who underwent surgery and remained hospitalized, is scheduled for a court appearance Monday. It wasn't clear whether he had an attorney to speak on his behalf. A message left with the federal public defender's office in Pittsburgh wasn't immediately returned.
Of the six survivors, five remained in the hospital Sunday, and two were listed in critical condition.
The nation's latest mass shooting drew condemnation and expressions of sympathy from politicians and religious leaders of all stripes.
Pope Francis led prayers for Pittsburgh in St. Peter's Square.
"In reality, all of us are wounded by this inhuman act of violence," he said. He prayed for God "to help us to extinguish the flames of hatred that develop in our societies, reinforcing the sense of humanity, respect for life and civil and moral values."
German Chancellor Angela Merkel's spokesman quoted Merkel on Twitter as offering her condolences and saying that "all of us must confront anti-Semitism with determination -- everywhere."