Three Saturdays each month, Pittsburgh's Tree of Life synagogue hosted a service specifically for children known as the junior congregation.

On those days, a group of kids would first gather in the lobby, and Stephen Weiss, a public school teacher and a synagogue youth leader, would then lead them in services, he said.

October 27, 2018, was not one of those Saturdays.

That miraculous coincidence was revealed in court Thursday at the federal hate crimes trial of the man accused of storming into the synagogue that day and fatally shooting 11 people and wounding several more.

Robert Bowers, 50, has pleaded not guilty to 63 charges, including obstruction of free exercise of religious beliefs resulting in death and hate crimes resulting in death.

Prosecutors say he carried out the attack because of his hatred for Jewish people and their perceived support of a non-profit that supports refugees. His defense has stated he was responsible for the shooting but in opening statements sought to raise questions about his motive and intent in the attack.

If Bowers is convicted, the trial will move to the punishment phase, during which the jury will have to decide whether to sentence him to death.

Over three days, the trial has featured harrowing testimony from the congregants who gathered at the synagogue that day and survived.

On Thursday, Weiss testified that he heard a "loud crashing sound" on the day of the shooting that he assumed was someone dropping a dish or breaking glass accidentally. Irving Younger and Cecil Rosenthal left the room to help -- and then Weiss heard four or five gunshots.

"To me, it sounded like a semi-automatic weapon," and the casing looked like a long gun, he said. "As I was standing in the door, I could see (shell casings) bounce on the floor directly in front of me."

He ran away from the gunfire and went downstairs to warn others, and then eventually escaped outside safely.

The Shabbat service that day was not completed, and Tree of Light sometimes has trouble getting the necessary 10 people together for services ever since. They don't have the same attendance, Weiss said, "because they've been killed."

Rabbi says he found hidden door to escape

Rabbi Jonathan Perlman of the New Light Congregation, which gathered in the Tree of Life building, testified that he heard shattering glass and gunfire as services were just beginning.

He crawled, swooped down low, and went into a room to hide, he said.

"It was an instinct, I've never been to any -- what do you call them -- trainings," he thought, "if somebody comes into the room we would avoid being hit if we were low to the ground."

He lost his glasses and his yarmulke while fleeing. He and several others, including Melvin Wax, went into a hidden closet space that Perlman said he had only discovered seven days earlier.

Perlman said Wax was hard of hearing and at a certain point went to open the door to the closet, assuming the risk was over.

"I don't know whether he heard noise, I don't know whether he understood what we were doing," Perlman said. "He says, 'Whatever it is it must be over, I'm going to go out and see what it was.'" Perlman said he told Wax to stay inside and hide, but "he wouldn't listen to me."

Wax, an 87-year-old accountant, was shot and killed.

Eventually, Perlman found a back door that he had never seen before that led him outside to a neighboring yard.

"I was really, really scared and I thought maybe I could get some help somewhere and all of a sudden I saw this door," he said. "It must have been created as an emergency exit of some sort."