Investigators also reviewed video from another major outlet where red dot black powder was also purchased.
Heisler has cooperated in the investigation, the release added.
McWhorter presented evidence to the Wilson County grand jury on Monday, April 11 which handed down the indictment against Heisler.
“This investigation was a cooperative effort, and we appreciate the effort by the two special agents and our Detective Division. This is considered by me to be a very serious incident that could have endangered the lives of many people, especially in the Watertown area,” said Sheriff Terry Ashe.