The Prison Service is investigating how an inmate with a history of violence obtained a knife before allegedly fatally stabbing another prisoner.
41-year-old Graham Johnson from Bandon died after suffering wounds to the chest and throat after a row in Cork prison on Saturday evening.
The victim was serving a four-year sentence for theft, and was due for release in a matter of weeks.
It is being reported that the suspect is being held in isolation while the investigation continues, and that the stabbing was witnessed by a number of staff and inmates.
The individual involved is said to be in his 30s, has a history of violent conduct and a history of serious drug addiction.