PITTSBURGH (AP) -- A survivor of the Pittsburgh synagogue massacre described Sunday how he and other terrorized worshippers concealed themselves in a supply closet as the gunman stepped over the body of a man he had just shot and killed, entered their darkened hiding spot and looked around.

"I can't say anything, and I'm barely breathing," recalled Barry Werber, 76, in an interview with The Associated Press. "He didn't see us, thank God."

The gunman, Robert Gregory Bowers, opened fire with an AR-15 rifle and other weapons during worship services inside Tree of Life Synagogue, killing eight men and three women before a tactical police team tracked him down and shot him, according to state and federal affidavits made public on Sunday. He expressed hatred of Jews during the rampage and later told police that "all these Jews need to die," authorities said.

Six people were injured in the attack, including four officers. 

Bowers 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.

As authorities worked to piece together Bowers' background and movements, harrowing accounts from the survivors began to emerge.

Speaking at a vigil in Pittsburgh on Sunday night, Tree of Life Rabbi Jeffrey Myers said about a dozen people had gathered in the synagogue's main sanctuary when Bowers walked in and began shooting. He said seven of his congregants were killed.

"My holy place has been defiled," he said.

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 who spoke Sunday on condition of anonymity.

US Attorney Scott Brady in Pittsburgh said Sunday night that federal prosecutors intend to pursue the death penalty against Bowers.

Bowers was a long-haul trucker who worked for himself, Brady said.

Little else was known about the suspect, who had no apparent criminal record but who is believed to have expressed virulently anti-Semitic views on social media. It appears Bowers acted alone, authorities said.

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. "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. 

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."

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 .

In the basement, a half-dozen members of New Light Congregation were just starting to pray when they heard crashing sounds coming from upstairs, looked out the door and saw a body on the staircase, Werber, the survivor, recalled Sunday in an interview at his home.

He said Rabbi Jonathan Perlman closed the door and pushed them into a large supply closet. As gunshots echoed upstairs, Werber called 911 but was afraid to say anything, for fear of making any noise.

When the shots subsided, he said, Melvin Wax opened the door, only to be shot and fall back inside.

"There were three shots, and he falls back into the room where we were," he said. "The gunman walks in."

Apparently unable to see Werber and the other congregants in the darkness, Bowers walked back out.

A day later, Werber called the gunman "a maniac" and "a person who has no control of his baser instincts."

"I don't know why he thinks the Jews are responsible for all the ills in the world, but he's not the first and he won't be the last. Unfortunately, that's our burden to bear," Werber said. "It breaks my heart."

The massacre came at a time of increasing anti-Semitism in the US Earlier this year, the Anti-Defamation League reported a nearly 60 percent rise in anti-Semitic incidents in 2017 -- the largest single-year increase since the ADL began its tracking nearly three decades ago.

Perlman, who also spoke at the vigil Sunday night, said New Light lost three congregants.

"These three men, they cannot be replaced," said Perlman, his voice breaking. "But we will not be broken. We will not be ruined."

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 US 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. US Attorney General Jeff Sessions said the charges could merit a death sentence.

Bowers, who underwent surgery and remained hospitalized, is scheduled to appear in court 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."