LUMBERTON, N.C. -- Authorities have arrested 10 North Carolina volunteer firefighters and accused them of setting fire to abandoned buildings and woods over two years. Robeson County Sheriff Ken Sealey said in a statement Tuesday the firefighters were from the Fairmont Rural and Orrum fire departments, and were involved in a conspiracy to set the fires.

The sheriff said there are approximately 90 arson-related charges in the investigation with more charges expected. Officials said that hundreds of thousands of dollars were wasted responding to the fires in Robeson County, near the state's border with South Carolina, reports CBS affiliate WNCN.

Sealey said a former Maxton police officer and a N.C. Department of Corrections officer were among those arrested.

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Sealey's statement didn't cite a motive. None of those charged have been identified.

Speaking Tuesday, North Carolina chief state fire marshal Brian Taylor couldn't specify how many incidents were being investigated and when they were reported.

He said his department is assisting in the investigation. Taylor said he's investigated cases in his career of firefighters setting fires, which he called "disturbing," but said "it does happen." However, he said, the number of firefighters accused in this case is unusual.

The investigation spanned a year and included the North Carolina State Bureau of Investigation, Alcohol Tobacco and Firearms, and the North Carolina Forestry Service.

Bail for the former police officer and corrections officer is set at $200,000. Bail for the others is $100,000.

All 10 suspects will make their first court appearances Wednesday morning, authorities said. More arrests are expected.