The man shot at a Pine Bluff gas station after he approached another car was a county constable, Tommy Holcomb, Fox 16 says. Reports have described this arising from "road rage." More available if you look quickly at Pine Bluff Commercial, which has a pay wall. He's the brother of County Judge Mike Holcomb.
Constables are constitutional offices and they have the power to patrol highways and make stops in the townships they serve.