DOYLINE, La. — The cleanup of 3,000 tons of explosives haphazardly stored at a munitions plant has frayed the nerves of residents who evacuated, closed the high school and spawned a criminal investigation of the company that owns the materials.

Authorities said about half the town’s 800 residents had heeded requests that they leave during the cleanup that started Saturday, but some appeared to be returning to their homes.

State police say some of the propellant was found spilling out of boxes crammed into buildings, and they have opened a criminal investigation into why the materials were not stored in bunkers at the state-owned site, leased by Explo Systems.

State police said the material is stable and would need an ignition source to explode.

Col. Mike Edmondson, commander of Louisiana State Police, said that Explo Systems leases and controls about 400 acres of the 15,000-acre Camp Minden, a former ammunition plant that now is a state-owned industrial site and home to a National Guard training facility. He estimated that the M6 propellant was stored in an area of less than 10 acres.

Explo has not publicly commented on the investigation. Neither a company executive nor an attorney who represents the company returned calls Monday.

Authorities had initially estimated the total of M6 stored at the site at 1 million pounds after the first investigator saw cardboard boxes on long rows of pallets behind a building. Police found more stacked in sheds and warehouses when crews returned Saturday to begin moving the boxes into bunkers about two miles away on the former munitions site.