The Mercer County's Prosecutors Office Homicide Takes Force is set to lead the investigation, due to their being an officer-involved shooting.
At least 20 have been injured, 16 from gunshot wounds. A 13-year old boy is in critical condition. More victims were at Capital Health Systems in Trenton.
"It absolutely could have been worse", Mr Onofri said. Attendees reported a heavy police presence at the site after midnight and up to the time of the 2:45 a.m. shooting.
One suspect was killed and a second suspect is in police custody, authorities said.
Onofri said the shooting appears to be related to a dispute among people at the event, and police confiscated several weapons. Irving Higginbotham was one of those injured.
"Everybody was having a nice time", he told Action News.
When she was walking back to her vehicle after the shots ceased, Darisme said she saw someone bleeding on the ground, in handcuffs.
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Across the border, Zaev has also met with opposition, with President Gjorge Ivanov saying he will not sign off on the agreement. But the agreement still needs to be approved by both parliaments and by a referendum in Macedonia.
"It was a pushing match at the door", witness Angelo Nicolo told WPVI-TV.
"People were running to him, trying to see his face, to see if he's a family member or a friend", she said.
Onofri says three of the four critically injured people have been upgraded to stable condition; the one remaining critically injured man "is believed to be a suspect in this matter".
"I saw two police officers escort a guy that got shot in the leg". "It was pretty gnarly". Trenton fire crews as well as medics, including some from Bucks County, have been called to the area.
There are also reports of an attempted carjacking nearby but it is not clear if it was linked to the shooting. The cause of the other injuries wasn't clear, but the gunfire caused mass confusion and panic as people fled the scene into the surrounding streets.
The New Jersey shooting occurs amid a debate about US gun laws that was given fresh impetus by the massacre in February of 17 people at a high school in Parkland, Florida. The remainder of the festival has been cancelled. The event began Saturday afternoon and was scheduled to conclude Sunday afternoon. The event showcases work by local artists, music and food.