Serial killer Robert Black refused to enter the witness box and look the jury in the eye in his latest murder trial because he knows he is guilty, a court has heard.

The prosecution has claimed the notorious paedophile realised he could not answer the questions the Crown wished to ask him about the abduction and murder of nine-year-old Jennifer Cardy.

Crown lawyer Toby Hedworth concluded a powerful closing address at Armagh Crown Court on Friday by urging the jury members to ask themselves why the 64-year-old convicted triple child killer would not enter the witness box.

The speech had to be interrupted at one point because a female juror broke down in tears as Black's dark criminal past was outlined.

He said: "There is one absolutely central and fundamental witness that I on behalf of the prosecution would have liked to ask some questions.

"Questions to assist you in your careful and thorough and fair examination of this case.

"But strangely this witness is not dead. He is not infirm. He is not unable to come to court. He has in fact been here in the centre of this court for the duration of the trial.

"But he has quite deliberately chosen not to walk the few short paces from the dock to the witness box - you can make your own assessment, but I make it eight paces - take the oath, look you in the eye and answer these charges.

"You may ask yourselves why? Because ladies and gentlemen the prosecution would have some questions for Robert Black. Questions that, because he is guilty, he knows he cannot answer."

Black, a former London-based delivery driver, denies kidnapping and murdering Jennifer while on a day-long work trip to Northern Ireland in August 1981.

On the 18th day of the trial, Mr Hedworth reiterated that the particular circumstances of the murder were wholly unique in the region over the last 40 years.

The schoolgirl's parents Andy and Patricia, her brothers Mark and Philip and sister Victoria watched the two-and-a-half-hour closing address from the public gallery.

Mr Hedworth said: "In Northern Ireland Jennifer Cardy stands alone - she is unique. No-one here does that sort of thing. But Robert Black does. And Robert Black was here on that day."

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.

Mr Hedworth said Jennifer's case bore the paedophile's criminal signature.

He told the jury: "That Robert Black was the abductor and murderer of Jennifer Cardy we submit you can and should have no doubt."