The South African Prisoners' Organisation for Human Rights (Sapohr) has demanded that an independent group with "no links to the South African prison system" be appointed to investigate last week's jail death at Pietermaritzburg New Prison.
Inmate Senzo Mazibuko, 28, died in the prison hospital on Monday after an alleged beating by warders. On the Sunday before his death he had been involved in a fight with a fellow inmate.
Sapohr president Golden Miles Bhudu said the matter reached Sapohr via "progressive correctional services officials" who do not want to be part of the killing of inmates.
"This whole thing would have been swept under the carpet had it not been for the courage of such officials. We have information that senior officials wanted the matter swept under the carpet because one of the warders involved is related to a senior prison manager."
The Department of Correctional Services has condemned the incident and said an investigation was under way by the police and the department.