MINDEN, La. — Just before midnight on Oct. 15, 2012, Sheriff Gary Sexton of Webster Parish was driving home from the airport when the sky lit up like midday. He flipped on his walkie-talkie to hear everyone asking: What on earth were those big booms?

As the sheriff would soon learn, two massive explosions had taken place at Camp Minden, a 15,000-acre site owned by the state in the pine woods just south of here, where private companies engage in military-related work. When the authorities began examining the blast site, they found something startling: thousands of tons of M6 propellant, used in the firing of artillery rounds, stuffed into plastic bags and piled into sagging cardboard boxes, many of them out in open fields.

“Turned upside down, spilled, out in the open, in the weather, out in the woods — it was unbelievable,” Sheriff Sexton said. “To be honest with you, I was ready to leave.”