"We left no stone unturned," he said. "This was not a suspicious fire."
Investigators reviewed pre- and postfire photographs and videos, used sophisticated arc mapping, and conducted interviews with property owners and fire scene witnesses. They also looked at possible financial motives, and analyzed fire-scene debris and the mechanical infrastructure in the section of boardwalk where the fire occurred to determine whether criminal activity was involved, Coronato said.
Ultimately, investigators determined that the wiring, installed after 1970, was compromised by severe wave action and saltwater flooding during Sandy, said Jessica Gotthold, a senior special agent with the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives.
The wires came in contact with each other and caused the electrical arc that started the fire, Gotthold said.
Coronato acknowledged that it can never be fully determined precisely how those wires came in contact, or whether the age of the wiring or the damage from Sandy caused them to fail. "We will never know," he said.
The section of boardwalk in Seaside Park where the fire started sustained almost no surface damage during Sandy. But farther north in Seaside Heights, entire sections of the wooden walkway - and the buildings and amusements that stood on them - were washed out to sea.
It was only by destroying a 25-foot section of the Seaside Heights boardwalk that had been rebuilt five months ago that firefighters were able to create a fire break.
Additional analysis and reporting by other agencies will likely determine liability for the blaze in terms of whether the boardwalk building should have been rewired or brought up to current codes following the storm, Coronato said.
"Today, I can confidently bring some sense of closure to this tragic event, affording the many owners of the destroyed and damaged businesses the ability to now take measures to rebuild and recover. This was not a criminal act," Coronato said.
He noted that the location where investigators found the spot where the fire apparently started - in the underground northeast quadrant of a building that housed Kohr's Frozen Custard and Biscayne Candies - was inaccessible, Coronato said.
"You'd have to tear down the entire building to get to that spot," he said.
"I'm sure on every boardwalk everywhere [at the Shore], there could be some compromised wiring," Coronato said. "We had a major storm."
Coronato said his portion of the investigation dealt only with whether there was criminal intent with the fire.
He said responsibility for who was required to maintain the underground wiring would likely be determined by further inspection and reporting by other agencies conducting their own investigations.
The municipalities of Seaside Park and Seaside Heights own their own boardwalks.
The spot where the fire started had been "submerged in salt water and wave action" during Sandy, Coronato said.
During the afternoon news conference at the Ocean County Library, the prosecutor recommended that any property owners whose homes or businesses were affected by the storm have the electrical wiring inspected to determine if the equipment has been compromised.
Immediately following the storm, fires were reported along the New Jersey coast in vacant homes and businesses where flooding had occurred. Salt water can corrode wiring, causing it to short out, spark, explode, and catch fire, officials said.
"We don't want to start a panic mode. We just want to be reasonable," Coronato said. "What we're saying is that if you're a property owner and you think your electrical work came in contact with water and sand, we strongly recommend that you have it inspected. Make sure your property is safe."
The findings raised concern among some business owners whose properties survived Sandy and the blaze.
"We thought we were good after the storm and repaired everything," said Derrick Johnson, whose family owns Slam, a boardwalk T-shirt shop in Seaside Heights that had to be refurbished after the storm. "Now we really can't be sure . . . because who knows what's really happening underneath the boardwalk."
Contact Jacqueline Urgo at 609-652-8382 or firstname.lastname@example.org. Read the blog "Downashore" at inquirer.com/downashore. Follow on Twitter @JacquelineUrgo.