Investigators are digging through evidence after two helicopters collided midair near Hammonton Airport, killing one pilot and seriously injuring another who later died Monday.

The crash happened just before 11:30 a.m. Sunday, according to The National Transportation Safety Board.

The NTSB and the Federal Aviation Administration are leading the investigation as eyewitness accounts continue to come in

Kenneth Kirsch, 65, and Michael Greenberg, 71, were friends who both lived in New Jersey and would often have breakfast together at a cafe near the crash site in Hammonton, about 35 miles (56 kilometers) southeast of Philadelphia.

Sal Silipino, who owns the Apron Café at Hammonton Airport, said he watched the crash as it happened.

“I saw one go down, I saw the other one go down – and it was a little bit of disbelief, like, is that really happening?” Silipino said. “I put on my coat, I went out there, and I saw the smoke and all and said, ‘this really happened.’”

Silipino said the pilots were friends and frequent customers at his café and had eaten breakfast there shortly before taking off.

“We saw them take off. We watched them for a while,” he said. “One was a little further from the other guy. They always fly together. We turned around, we were talking. We looked up, I saw the one spiraling down.”

Hammonton Police Chief Kevin Friel said in a statement that Kirsch, of Carney’s Point, was pronounced dead at an area hospital after being flown there, while Greenberg, of Sewell, died at the crash site.

Lighting was staged at the crash site Monday morning. Officials said after initial examinations, debris will be transported to a secure facility for further examination.

The investigation will include a review of aircraft maintenance records, communication data, and witness statements, among other factors.

“They looked fine. They looked good. It’s hard to believe,” Silipino said.