Child serial killer Robert Black's horrific criminal past has been revealed to a stunned jury at his trial for the murder of another schoolgirl.

The paedophile was unmasked as Armagh Crown Court heard, for the first time, that the Scottish van driver has already been convicted of murdering three young girls, abducting a fourth and attempting to snatch another.

Sex attacker Black, 64, now stands accused of kidnapping and murdering nine-year-old Jennifer Cardy in Northern Ireland 30 years ago. He denies the charges.

Jennifer was abducted as she cycled to a friend's house in the quiet Co Antrim village of Ballinderry in August 1981. Her body was found six days later floating in a dam 10 miles away near Hillsborough, Co Down. She had been sexually assaulted.

Legal reasons had prevented the killer's criminal record being disclosed to the jury during the first eight days of the high profile trial.

But that changed during a dramatic day in No.1 Court in Armagh as Crown lawyer Toby Hedworth QC outlined in graphic and shocking detail exactly what the man sitting in the dock had been found guilty of.

"The stage in the trial proceedings has been reached when I can tell you," he told the jury at the outset of his address.

With an impassive Black listening to proceedings with the aid of a special hearing device, Mr Hedworth revealed the defendant had been convicted of murdering three girls in the 1980s - Susan Maxwell, 11, Caroline Hogg, five, and 10-year-old Sarah Harper - and the attempted kidnap of a 15-year-old girl in 1988.

The lawyer said the London-based delivery driver's reign of terror ended in dramatic fashion in 1990 when he was arrested near Stow in Scotland with a six-year-old girl gagged, bound and stuffed head first into a sleeping bag in the back of his van. He was convicted of her abduction after pleading guilty.

Police subsequently linked him with the three murders, the attempted abduction of the 15-year-old and a series of other charges.

He denied the counts but was found guilty of them all at a 1994 crown court trial in Newcastle Upon Tyne.

Mr Hedworth said his past crimes did not in themselves make Black guilty of Jennifer's murder, but claimed the striking similarities between the cases would prove it.

He urged the jury: "What you certainly must not do is say 'well he's done those other ones, he's a thoroughly bad man so we'll find him guilty in this case as well'.

"What you have to do is look at what he has been proved to have done in respect of those other girls and see whether it assists you in deciding whether you can be sure that it was Robert Black rather than some other individual who abducted and killed Jennifer Cardy.

"The prosecution will submit that the similarities between Jennifer's case and those other cases make it clear that they were in fact the work of the same man."

Jennifer's parents Andy and Patricia, at some points visibly emotional, watched from the public gallery as Mr Hedworth went on to detail Black's history.

Black, whose work in the 1980s took him all over the country in his delivery van, denies kidnapping and murdering Jennifer.

Mr Hedworth said while he denied the crimes he was found guilty of in the past - apart from the kidnapping in Stow when he was "caught red handed" - he did admit to police in 2005 that he fantasised about abducting pre-pubescent girls and having sex with them in his van.

The court then heard highly disturbing details of what Black told officers he dreamed of doing to the girls. Mr Hedworth said Black had never admitted that "his behaviour ever moved from the fantasy to reality in a sexual way".

He added: "There comes a point beyond which he is simply not prepared to face what he has done."

But he told the jury the scenarios Black admitted dreaming about had distinct similarities with the circumstances of Jennifer's disappearance.

"Standing back from these lengthy interviews in 2005 the prosecution will submit to you that they contain a partial or perhaps even coded admission to Jennifer Cardy's abduction and murder by a man who cannot bring himself to admit to the enormity of his behaviour."

Earlier, Mr Hedworth, who is prosecuting with junior Crown counsel Donna McColgan, described the murders of the other girls.

Susan Maxwell went missing as she walked between the villages of Cornhill-on-Tweed and Coldstream on either side of the Scottish/English border after playing a game of tennis in July, 1982.

Her body was found dumped by a roadside near Uttoxeter, Staffordshire 260 miles away. Police suspected a sexual assault.

A year later in July 1983, Caroline Hogg vanished as she played near her home in Portobello, close to Edinburgh. Her body was found in a ditch in Leicestershire, 300 miles away, ten days later. A sexual assault was again suspected.

In 1986 Sarah Harper disappeared after leaving her home in Morley near Leeds to buy a loaf of bread in a corner shop. She vanished on her way home.. Her body was found floating in the River Trent near Nottingham a month later. She had been raped.

All the bodies were recovered in relatively close geographical proximity.

Black was also found guilty of trying to abduct a 15-year-old girl in Nottingham in April 1988. She managed to fight off his advances.

Mr Hedworth said the Crown contends there are at least 12 distinct similarities in the various cases.

The lawyer said these patterns, along with the particular nature of Black's fantasies, made a compelling case and provided a "signature of offending".

The prosecution insist work records and documentation proves Black was in Northern Ireland on the day of Jennifer's murder doing a delivery run.

Mr Hedworth concluded: "When you add to Robert Black's availability in the area of both Jennifer's abduction and the deposition of her body, at the times that both must have taken place, the full picture that you will have of him being one of those exceptionally rare, indeed almost unique, individuals who target girls of a particular age to steal them away from the roadside in a vehicle for sexual purposes and then dispose of their bodies when he has no further use for them, in a way and in locations that carry what amounts to a signature of his offending, it will be the prosecution's submission that Jennifer Cardy's killer was this defendant, Robert Black."

The trial continues.