Two students face expulsion after police discovered a shotgun inside the trunk of a car parked on the campus of a charter school for at-risk students.

Joshua Brown and Zia Fredericks, both 18, were arrested and charged with possession of a weapon on school grounds Monday. The Greg Mathis Charter School students told authorities they carry the gun with them wherever they go for protection, according to a police report.

The report says the school's student concern specialist overheard several students talking about a gun in the trunk of a gold Ford Crown Victoria. When the employee questioned the students about the gun, Fredericks said it was his gun in Brown's car.

A North Charleston Police officer found the unloaded 12-gauge shotgun in the trunk along with five shotgun shells.

Fouchina Kirkendoll, the school's chief operations officer, said the students have been suspended pending an expulsion hearing.

She said there's no evidence the students intended to harm anyone at the school.

"It was an isolated incident," she said. "We put the school on lock down. The students were arrested and taken off campus."

The Greg Mathis Charter School, formerly known as the YouthBuild Charleston Center, has 106 at-risk students from around Charleston County, Kirkendoll said. The school gives many students a second chance while others benefit from smaller class sizes, she said.

"We're no different than regular schools and some of the issues they deal with," she said.

Brown and Fredericks were both released from the Charleston County jail Tuesday on $5,000 bond. Neither student could be reached Wednesday.