The 3:30 p.m. explosion shook the ground for miles and sent debris flying across all four lanes of White Horse Pike.
Another resident was taken to Our Lady of Lourdes Medical Center in Camden. Police said her injuries were minor.
On Sunday afternoon, the charred remains of the five-unit apartment building, fenced in by a restoration crew, had become a spectacle for neighbors and passersby. A variety of items was strewn about the yard: piles of wood, broken window frames, a purple exercise ball, a wig, clothes entangled in tree branches, a fire extinguisher.
"Oh, my God. Oh, my God," neighbor Judy Liby whispered as she walked by. "Just seeing the debris -," she mused.
Nunn's cat, a black Maine coon with green eyes, was believed to have escaped the building, and Nunn's friends were still looking for him Sunday morning, police said.
PSE&G spokesman Mike Jennings said there were no reports before the explosion of outages or service problems at the building.
Utility crews cut off service to the building Saturday and on Sunday were still investigating, Jennings said.
Haddon Heights Mayor Edward S. Forte Jr., also a longtime volunteer firefighter, said a gas leak that size should have had a strong odor.
"I would imagine it wasn't leaking in the exterior of the building or hadn't been leaking for a long period of time, or else people would've smelled it," he said. "I didn't hear any reports of people who smelled gas."
The Haddon Heights Police Department issued a statement Sunday morning thanking those who helped residents out of the building and "most likely saved the life of one of the victims."
Police declined to identify the Good Samaritans, but in an interview with 6ABC Saturday night, passerby Jessica Pastoriza described running into the building to find a woman screaming on the second floor.
"When I was inside, I couldn't see anything. I felt the heat," Pastoriza said. "I hear, 'Help me, help me.' I ran out, I see a girl on the second floor, ripping her clothes off, and her skin's coming off with it," Pastoriza, 20, said.
County spokesman Dan Keashen said that by the time he arrived, the building was a burned-out shell. "That was far and away the wildest thing I'd ever seen, from an emergency-management perspective," he said. "The apartments were gone, down to the first floor."
Witnesses said the fire started several minutes after the explosion. Soon after, the remaining floors pancaked to the ground.
Forte said he had never seen an explosion that size. "We're very fortunate that there weren't more people in the building at the time."
Contact Jessica Parks
at 610-313-8117, email@example.com, or follow on Twitter @JS-Parks.