Authorities say seven vehicles have been stolen and set on fire in Caroline County since mid-July. Recently, two vehicles were found burning, one near Henderson and the other in Greensboro. A third was found burned in the northern part of the county over the weekend. Most of the fires were started by lighting a flammable substance in the passenger compartment. The arsons have mystified authorities in the rural Eastern Shore county. State police have teamed up with the Caroline County Sheriff’s Office and the State Fire Marshal’s office to investigate the series of fires. Police are reminding residents to keep their cars locked and their keys in secure locations.