A 29-year-old man has gone on trial at the Central Criminal Court accused of stabbing to death a fellow inmate at Mountjoy Prison in Dublin in 2007.

Declan O’Reilly from Parnell Road in Crumlin has pleaded not guilty to the murder of Derek Glennon on 25 June 2007.

The court heard that the killing happened quickly and was unusual because it took place in prison and was captured on CCTV.

24-year-old Derek Glennon died in the Mater Hospital after he was stabbed while on the ground floor of D-Wing at Mountjoy.

The CCTV footage, which was played in court this afternoon, showed a fight break out between Declan O'Reilly and Derek Glennon at around 5.35pm on 25 June 2007.

The chief prison officer in charge of the wing that day, John Farrell, said he first thought it was horseplay but when he got to the scene outside Derek Glennon's cell, it looked like Glennon had subdued Declan O'Reilly.

He said he removed Glennon but the prisoner remained violent and refused to stop.

Mr Farrell said he then heard a colleague shout ‘he has a knife’ and he struck Derek Glennon on the face to subdue him and laid him on his back, which was normal procedure.

The prisoner officer told the court that at that point Derek Glennon told him he had been stabbed and when he lifted up his sweatshirt he could see a large wound on his chest.

Mr Farrell said the prison officers did the best they could for Derek Glennon until medical staff arrived.

The court heard that Derek O’Reilly was taken to a basement holding cell where he was treated for a serious hand injury.

The trial continues.