The prisoner, who was serving time for a second-degree robbery, was found dead in his cell Sunday after guards found him unresponsive.
When guards went to inspect his bunk, they found the decedent under his blankets and efforts to revive him were unsuccessful.
He was declared dead at the scene, Sheriff's Deputy Lillian Peck said.
Coroner's officials later inspected the body and found "something suspicious," but did not elaborate further.
Authorities are not releasing the name of the victim or his cellmate.
This death is the fourth suspected homicide in the state since October, according to the Department of Corrections and Rehabilitation.