The 24-hour “Art All Night Trenton 2018” arts festival in Trenton, New Jersey turned violent just before three in the morning on Sunday when gunfire suddenly erupted.

At least two gunmen opened fire, injuring 22 people, including a 13-year-old boy, according to the Washington Post.

A responding police officer fatally shot one of the suspects — the other gunman was arrested.

The shooting is believed to be gang-related.

“We believe it was a dispute between two neighborhoods that led to violence at the event. In no way was the event the target, it just happened to be the forum for the shooting,” Mercer County Prosecutor Angelo Onofri told ABC News.