State Police said former Carter County Sheriff's Deputy Matthew Morrison, 38, of Grayson, didn't serve an arrest warrant on someone in exchange for sexual favors while he was on the force.
Investigators also said Morrison engaged in several illegal transactions involving controlled substances (pills) while on the force.
Morrison had already been fired from the Sheriff's Department before the State Police investigation began in February 2014.
State Police said the investigation was ongoing.
Morrison was lodged in the Carter County Detention Center.