Cox asked the public for help in identifying the attacker. As of Sunday evening, no one had been arrested.

“This is a pretty large crime scene that we will be reviewing for most of the evening, so the area on Circuit Drive will be cordoned off for a while,” Cox said.

“However, there were many, many witnesses and we need the public’s assistance in this matter,” Cox continued. “If anyone has any video footage or anything like that, we really need help in this case because we need to hold these people accountable.”

Cox said the violence “really marred what was a pretty successful event for the people here.”

On Sunday evening, the park was a chaotic affair as police investigated the shooting, the crowds dispersed, and festive music played from the waning celebration.

Jaden Peguero, 19, spent the day at the festival. Shortly before 9 p.m., he heard gunshots about “a 10-minute walk” away, he said.

Peguero said gunshots were heard, then police immediately arrived and began escorting people out of the venue.

As he sat on a bench on Franklin Road, the street blocked off by police vehicles, he reflected on the violence. “Nobody is shocked,” he said.

In 2012, 22-year-old Sharrice Perkins, Kristen Lartey and Genevieve Phillip were shot dead in a parked car after attending the Dominican Festival. In recent years, however, there have been no major outbreaks of violence at this festival.

On Sunday evening, Arthur Martinez and Sophia Diaz, both 20, sat in Franklin Park with a group of friends, many of them wearing Dominican flags around their shoulders or waving small flags in their hands.

The couple said they were “right there” when the shooting occurred, but only later learned that someone was injured.

“The only thing I saw was people shooting in the air,” Martinez said, expressing surprise that five people were taken to the hospital.

“We just started running,” Diaz said. “It was crazy.”

Diaz said the event had just ended and “everyone had left” when the gunfire erupted.

“I thought it would be cool,” she said, shaking her head.

By 9:45 p.m., the crowds continued to pour out of the park onto Blue Hill Avenue. Many families left the park with tired young children in tow, and many held small Dominican flags. Music from the island nation blared through the streets from various sources.

Carly Pereira, 27, was at the festival when her car got a flat tire. She went to a parking lot outside the event to check, where she soon heard gunshots, she said.

“We didn’t see anything, we just heard the shots,” she said.

At around 10 p.m., Pereira observed police vehicles continuing to flood the area where the festival had taken place shortly before.

“This is nothing new,” she said of the violence.

Globe writer Mike Bello and correspondent Adam Sennott contributed to this report.

You can reach Ava Berger at [email protected]. Follow her @Ava_Berger_.