Joshua Jones died two days after he was assaulted at the Mountainview Youth Correctional Facility in Clinton Township.
The 23-year-old from Englewood was convicted of possession of a handgun and distributing drugs in a school zone. He would have been eligible for parole in January.
The Hunterdon County Prosecutor's Office says Jones was discovered in a dorm where several inmates reside. Authorities say they are aggressively investigating the case.