Martin was on remand for murder at the time of the attack

David Martin was captured on CCTV in June 2007 as he kicked and stamped on Michael Cameron at Kilmarnock Prison.

The judge said questions would be asked about why prison staff had failed to intervene, but Serco - which runs the private jail - defended its procedures.

The sentence at the High Court in Edinburgh also covered Martin's killing of Gilbert Grierson in March 2006.

Martin was sentenced to life after admitting murdering Mr Cameron and was told he would have to serve a minimum of 24 years before he could apply for parole.

That sentence also encompasses his period of punishment for killing Mr Grierson.

The 20-year-old had previously admitted culpable homicide by killing Mr Grierson, 46, with knives, scissors, a frying pan and a bottle and setting his home in Irvine on fire.

His attack on Mr Cameron happened three months after Martin was remanded for killing Mr Grierson, who was his mother's former boyfriend.

The attack happened in the prison's healthcare wing

The incident, in Kilmarnock Prison's health wing, also saw Martin pour boiling water over his victim.

Mr Cameron was on remand at the time, accused of rape.

A prison officer witnessed the murder but did not intervene until re-enforcements arrived.

Under prison protocol a total of three custody officers should restrain any one prisoner.

Martin's lawyer, Bill McVicar, described his client as a damaged individual who had a life of breathtaking deprivation.

But the judge, Lord Matthews, said Martin's background was not an excuse for his actions.

"You are no stranger to violence and it will be difficult to forget the CCTV images showing what you did to Mr Cameron," he said.

"I do not know what kind of warped morality made you think it was appropriate to act in that manner.

"No doubt questions will be asked and I know they are already being asked about the fact that this happened in prison while staff were watching."

'Tragic occurrence'

Serco spokesman Michael Clarke said: "There were four prisoners in the healthcare unit in a ward and there was one prison officer and one nurse in the immediate area when this horrific attack erupted.

"He quite rightly called for re-enforcements before entering the ward to stop the incident and within a couple of minutes extra staff had arrived."

Figures released last month by the Scottish Government showed a total of 225 prisoners had been assaulted at HMP Kilmarnock in the past seven years.

Last year, 49 assaults took place - a record number.

However, Mr Clarke said the Serco employees "did the right thing" and claimed that staffing levels at the prison were adequate.

"It was a tragic occurrence, a horrific attack and we need to make sure that we do everything to prevent it happening again," he added.