Robert Black guilty of fourth child murder

Victims: Jennifer Cardy and Black's Scottish targets

Evidence: the crucial petrol receipt

The lawyer: ending unfinished business

Photographs: police images and paper evidence

Audio: Hear an excerpt from Black's police interviews

The jury returned its verdict, Black's fourth murder conviction, at Armagh Crown Court on the second day of deliberation at the end of a high-profile five week trial.

The schoolgirl was snatched as she cycled to a friend's house in the quiet Co Antrim village of Ballinderry on August 12 1981.

Her body was found six days later in a dam behind a roadside layby 15 miles away at Hillsborough, Co Down.

In 1994, Black was convicted of three unsolved child murders in the 1980s - 11-year-old Susan Maxwell, from the Scottish Borders, five-year-old Caroline Hogg, from Edinburgh, and Sarah Harper, 10, from Morley, near Leeds - and a failed abduction bid in Nottingham in 1988.

Black's killing was finally ended in 1990 when he was caught red-handed by police with a barely alive six-year-old girl hooded, bound, gagged and stuffed in a sleeping bag in the back of his van in the Scottish village of Stow. He had sexually assaulted her moments earlier.

The jury took four hours and 15 minutes over two days to reach its verdicts. Black showed no emotion when the verdicts were read out.

Jennifer's mother Patricia sobbed quietly in the public gallery and was comforted by her husband Andy.

Judge Mr Justice Ronald Weatherup told Black: "You have been convicted by a jury of murder. There is only one sentence that will be imposed by law. That's the sentence of life imprisonment. Accordingly, I sentence you to life imprisonment."

Prosecutors could be asked to review another schoolgirl's disappearance linked to Robert Black in the wake of his conviction for Jennifer Cardy's murder.

The serial killer has long been the prime suspect in the case of missing 13-year-old Genette Tate, who was last seen in a country lane in Aylesbeare, Devon, in 1978. No trace of the newspaper delivery girl has ever been found.

Black has been questioned about her suspected abduction a number of times, but three years ago the Crown Prosecution Service decided not to charge the Scottish paedophile on the grounds of insufficient evidence.

But it is understood detectives from Devon and Cornwall Police have been closely monitoring events in Armagh Crown Court and today's conviction, in a case where crucial bad character evidence was allowed to be presented to the jury, could prompt them to submit another file to the CPS.

While Black has been linked to a number of other historic disappearances, a retired Scottish detective who has been investigating the killer for more than 20 years said Genette's was the only realistic prosecution left.

But former Lothian and Borders detective chief superintendent Roger Orr said he was sure the convicted quadruple child killer harboured many more secrets.

"Now you're only really probably talking about Genette Tate," Mr Orr said, in relation to the prospect of further prosecutions.

"It's not for me to say what will happen with Genette Tate, whether this (the latest trial) will kick it back in again or whether it will just finish at that point."

Black's current criminal record shows two convictions for sexually abusing young girls in the 1960s then a long gap before the first murder he committed - Jennifer's in Northern Ireland in August 1981. He also killed Susan Maxwell in 1982, Caroline Hogg in 1983 and Sarah Harper in 1986.

Mr Orr said there were undoubtedly questions over what he was responsible for in the gap between his abuse convictions and Jennifer's murder. "I can't fill the gaps," he said. "My gut feeling is there are gaps there, he's done more. That's easy to say, but it's much harder to prove and if the cases aren't there and forces don't have the commitment to push them then they aren't going to get looked at."

The ex-detective revealed that 40 cases were reviewed by police in the 1990s to assess Black's potential involvement. But he said he has been eliminated as a suspect from many of them. "He's not done them all, that's the thing," he said. "He's not a three-headed monster - he's a very, very dangerous guy, a very dangerous guy - but he's not done them all."

Mr Orr, 54, retired from Lothian and Borders Police in 2008 but still works as a liaison to help other detectives investigating the killer.

He assisted the Police Service of Northern Ireland team that compiled the evidence against Black for the Jennifer Cardy case but he insists the credit is all theirs.

"These guys who investigated this put the case together, not me," he said.

Mr Orr revealed that when he first interviewed Black in 1990 - when he was caught red-handed in the Scottish village of Stow with a barely conscious six-year-old girl in the back of his van - he believes he was on the verge of confessing to his crimes.

"He's not stupid at all," he said.

"He will engage you in a wide range of topics, when I interviewed him in 1990 we had a wide-ranging conversation to start with and it gradually came in and in and in.

"At one stage I was holding his hand across the table, towards the end of the interview, and I thought 'Yeah, I got you now, just need to put a wee bit more on here', but the tape went beep (to signal the end of the interview) and he just put his head down and that was it, finished."