ATF spokesman Michael Knight said it will now be up to the Tennessee Occupational Safety and Health Administration to determine fault and whether there were any safety violations at the plant.
The explosion Wednesday afternoon at Rio Ammunition killed Rodney Edwards and injured three others. Joey Clark was listed in stable condition at Vanderbilt University Medical Center on Saturday. The other two victims were discharged earlier in the week.
A news release from Rio parent company Maxam said the Tennessee plant produced shotgun cartridges, and the blast occurred during the company's cartridge loading operations.