"We have determined through our investigation, along with Wake County, that we had an accidental explosion due to a natural gas release," Durham said.
The gas leak was confined to the room only and ignited. The south side of the building was newer construction and there was a separation point from the north side.
"Inside that room there are several electronic components," Durham said. "There are circuit breakers, there's lighting, there's motors, there's fan motors, etc. Any one of those things could have ignited the natural gas that was released in the room."
On Friday morning, ATF agents began interviewing plant workers about what they saw and heard before and after the explosion as apart of the investigation process.
Durham said investigators interviewed about 150 employees and some said they noticed an odor of gas on the day of the explosion.
Click here to read background information about the deadly explosion
Officials said Saturday they were finally able to safely enter the room where the explosion occurred. Durham said they were able to determine the natural gas leak by tracing the gas lines to the room.
During the investigation, officials said they found the lines appeared to have been worked on and there was a separation of pipe. Some gaps in the piping may have allowed the gas to leak.
The snack food plant was in the process of installations for some time that involved changing out their stream system to an upgraded hot water system.
Durham said ATF did not find any criminal activity involving the explosion and was there for concluding the criminal investigation.
ATF will be turning over the investigation to the US Chemical Safety Board and the North Carolina Occupational Safety and Health Administration.
"Citizens of Wake County can rest assure they are in safe hands," Eric Copland with Garner Police said on Saturday when referring to the investigation process.
Officials said the transition of the investigation should hopefully provide more information as to what could have caused the natural gas release and ignition source.
AFT said they are meeting with ConAgra Foods to talk about the transition from the criminal investigation. They are releasing the plant back to the company's control now that their investigation is done.
The Wake County Emergency Communications Center is also in the process of compiling recordings of 911 calls and radio traffic from emergency responders on Tuesday. The recordings could be released to the public after the review.
Click here for more on the investigation
Click here to see images from the scene
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