Preliminary indications, DPS said in the statement, are Charles Moss may have been using a form of synthetic marijuana known as K2.
A correctional sergeant found Moss unresponsive just before midnight Wednesday, DPS said. Correctional staff initiated CPR and called EMS and the Halifax County Sheriff's Office. Attempts to resuscitate the inmate failed and he was pronounced dead shortly before 1 this morning.
DPS said an internal investigation has been launched and the sheriff's office will investigate.
The North Carolina State Bureau of Investigation has also been notified.
Moss was serving a 28-year sentence for second-degree murder in Lincoln County and was convicted in 2002.
A spokesperson for DPS was not immediately available for further comment and an official for the sheriff's office was not immediately available for comment.
