A murder investigation is taking place at HMP Risley in Cheshire following the death of an prisoner.
It is believed the inmate, named as 33-year-old Stephen O’Donnell, was stabbed on Tuesday evening.
Cheshire Police said he was taken to Warrington General Hospital, where he died.
A 23-year-old man was arrested on suspicion of murder.
A spokesperson for Cheshire Police said: "At 7.41pm on Tuesday 22 January police were called to reports of an assault at HMP Risley in Warrington.