BUFFALO, N.Y. — The fire at 745 Main Street in Buffalo's Theater District this past March that claimed the life of firefighter Jason Arno has been ruled as accidental, Erie County District Attorney John Flynn said during a press conference Thursday.

He said the ruling came from an investigation by the Bureau of Alcohol, Tobacco, Firearms and Explosives. Flynn explained the decision by saying there was no way to prove without a doubt there was gross negligence leading to Arno's death.

“If you have an action that occurs and then you have numerous links to the chain and then at the end of the chain a death occurs, I have to prove that not only the links of that chain are a direct correlation in a death, but on top of that, I've got to prove that nothing came in intervening and broke the chain of the links," said Flynn.

Flynn explained that construction workers using a blow torch and metal shovel to melt snow and ice on and around the building near a makeshift plywood door with combustible elements behind it led to the fire. Flynn said that the ATF determined sparks made their way around the gaps in the makeshift door and to the bags of combustibles behind it. The plywood door did not catch fire, it only charred.

Flynn added that no criminal changes will be sought stemming from the fire and Arno's death. 

Charles Desmond, the attorney for Arno's widow Sarah Tierney, told Spectrum News 1:

"We are handling the civil case. We will defer the DA and ATF in regards to criminal charges. That being said it is abundantly clear that the negligence of the contractor started the chain of events that lead to the death and suffering that Mr. Arno had to endure."

Firefighters initially responded to the location around 10 a.m. on March 1. The Main Street building held DC Theatricks, a professional theatrical costume rental company for stage plays and musicals.

Firefighter Arno’s body was recovered from the brick building several hours after he was reported missing early on in the fire. Fire Commissioner William Renaldo said Arno was 30 to 40 feet inside when he issued a mayday call, which led to the emergency evacuation of everyone inside. Arno was not heard from again.

Arno's official cause of death is smoke inhalation and thermal injuries.

It marked the first line of duty death in the Buffalo Fire Department in nearly 14 years.