It happened around 1:30 Saturday morning at the Mercer County Corrections Center in Hopewell.
Officers noticed water flowing from under the door of a cell.
When they arrived, they found the body of 38-year-old Darryl Boone. Standing nearby was his cellmate 19-year-old Lamar Gaines.
Officers apprehended Gaines and attempted to revive Boone but were unsuccessful.
Authorities say a preliminary investigation revealed that Gaines allegedly choked and suffocated Boone. There were also indications of a physical assault.
Gaines has been charged with murder and bail was set at $1 million.
Officials also report that Gaines was also involved in an incident on October 3 in the gym area of the correction center.
Another inmate was left hospitalized and Gaines was charged with attempted murder in that incident.
Boone's cause of death has not been revealed, pending an autopsy.