He said no charges will be filed.
Officials said the shooting happened when 36-year-old Gary Lynn Wilson, of Wilmington, brought a loaded shotgun in a case to a security checkpoint at The Dixie Gun and Knife Show Saturday.
As Wilson unzipped the case for inspection, officials said the weapon went off, striking three people, including a retired Wake County deputy working at the show.
The show continued Sunday, but private gun sales were not allowed.
It was one of three accidental gun show shootings nationwide over the weekend. There were also incidents reported in Indiana and Ohio.
Willoughby said he had scoured North Carolina statutes before reaching his decision. North Carolina does not have a reckless endangerment law. One was proposed in the Legislature in 2005, but it never passed.