A man has denied killing an inmate at a north London jail but told a court he did stab the prisoner's friend because "he was trying to stab me".
Jamal Mahmoud, 21, was killed in Pentonville Prison on 18 October last year in a row over contraband, the Old Bailey has heard.
Basana Kimbembi told the jury he stabbed Mohammed Ali with his own illicit hunting knife.
Mr Kimbembi, 35, Joshua Ratner, 27, and Robert Butler, 31, all deny murder.
The group also deny wounding with intent to cause grievous bodily harm.
Mr Kimbembi told the jury Mr Ali had a knife which looked "vey similar" to one he saw among a stash which were in the cell of a fellow inmate.
"It was a big knife in a sheath. I was curious. I had never seen that kind of weapon in prison," he said.
After Mr Mahmoud was killed the hunting knife was found discarded on the floor in G Wing, the court heard.
Mr Kimbembi told the jury "the Somalis" had control of contraband on the wing, referring to Mr Mahmoud, Mr Ali and their friends.
He denied knowing about any trouble with "the Somalis" before the killing and said he was never a member of a gang in the prison.
The court heard Mr Kimbembi, who takes medication for paranoid schizophrenia, has convictions for 15 offences including robbery and carrying a knife.
He told jurors he had come to Britain from the Congo at the age of 11 after civil war had broken out.
The trial continues.