INDIANA, Pa. — State police are still working to identify the gunmen who killed a Pittsburgh man and injured eight other people during a gathering at an Indiana County community center early Sunday morning.

A $15,000 reward is on the table for information leading to the identification and prosecution of the individuals responsible for shooting dozens of rounds into a crowd of over 150 people, police said during a Sunday afternoon media briefing.

Officers first caught wind of the unruly gathering at around midnight on Sunday, when they received noise complaints from neighbors adjacent to the Chevy Chase Community Center. The small, tan and white center borders several homes and a Veterans Community Garden space. It’s blocks away from the Indiana Area High School and about a mile from the Indiana University of Pennsylvania.

When officers arrived to the scene, they heard gunshots from within the building at around 12:30 a.m. Chaos then ensued, said Pennsylvania State Police Lt. Col. George Bivens.

“There were people running through that neighborhood. They exited that building in any way possible,” Lt. Col. Bivens said. “… People dove through windows, people ran through doors, ran through porch railings, trying to get away from that scene. There was chaos.”

Officers treated victims who rushed out of the building and collapsed, while others officers rushed in toward the gunfire. Numerous shell cases and multiple firearms were recovered from the scene. No officers were injured.

Though the White Township neighborhood was quiet Sunday afternoon, remnants of the night’s mayhem still engulfed the community center. Yellow police tape hugged its “free little library” that’s advertised with a sign featuring “The Very Hungry Caterpillar.” The police tape surrounded the entire building and prevented community members from entering its doors or peering through its windows decorated with Valentine’s Day stickers.

Items left behind by panicked partygoers or responding officers littered the center’s front lawn — including two Nike shoes, a combat gauze wrapper and an empty water bottle.

Police have not disclosed the purpose of Sunday’s gathering, but specified that the event was not sanctioned by IUP and it was not directly linked to this weekend’s homecoming celebrations. IUP officials have said two of the injured victims were IUP students.

The event was a “privately organized party,” Lt. Col. Bivens said. Attendees paid a fee with an app to get in.

Police believe the shooting was isolated to this gathering, and there is no threat to the public at large.

Six of the victims are men and three are women, police said. Six remained in the hospital Sunday afternoon, with at least one victim in critical condition. They are all between 18 and 23 years old. Police have yet to publicly identify the victims.

In addition to relying on tips from the public, police are also using doorbell camera footage, forensic evidence and transactional information from the attendance fee to investigate the shooting.

Those with information should contact Pennsylvania State Police at 724-357-1960.

“This is a very complex and spread-out crime scene that we continue to work through at this time,” Lt. Col. Bivens said. “Thousands of pieces of evidence have been and continue to be collected.”

The Chevy Chase Community Center was built over 50 years ago and has played an “integral part” in providing the people of Indiana with meals, shelter, support and a community atmosphere, said Indiana County District Attorney Robert F. Manzi, Jr., who also serves on the center’s board of directors. The center can also be rented out for private events like Sunday’s.

“It has served as a place to help members of our community for many decades,” Mr. Manzi said.

When the shooting happened, IUP sent an alert to students urging them to be vigilant and stay in a safe location. Alexis Bardos, an IUP freshman from Cranberry, was asleep during the incident, but said it was “smart” of the state university to send out the alert. She generally feels safe on campus.

“Honestly, I’m not very shocked [by the shooting] just because of society today. People get shot,” said Ms. Bardos, who studies biology. “But it was surprising that it was only a mile away from campus.”

Max Petrone, a senior from Moon, agreed the alert was “appropriate,” but added he doesn’t believe the university is responsible for the incident.

“It’s not the school’s issue, it’s more of a community problem,” said Mr. Petrone, who studies supply chain.

Carson Wendling, a senior studying supply chain from Hershey, expressed concerns that serious events like this one are becoming a “common theme” during the Indiana school’s celebratory weekends. He referenced the spring semester floor collapse of an off-campus apartment that injured 12 people.

“Every time there’s a big weekend, I feel like this always happens,” Mr. Wendling said.