28 May 2012 Last updated at 14:06 ET

Rebecca McKeown's grandparents acquitted of manslaughter

The couple have been acquitted of all charges

An elderly couple accused of killing their severely disabled granddaughter have been acquitted of all charges.

David and Sarah Johnston, from Carwood Drive, Glengormley, County Antrim, had denied manslaughter and child cruelty charges against Rebecca McKeown, 14.

The judge directed the jury to acquit the couple after the prosecution collapsed in the face of evidence that cast doubt on the cause of death and revealed a new possible cause of injury to Rebecca.

Rebecca's mother Cheryl - the couple's only daughter - collapsed outside the courtroom following the decision.

Rebecca died in hospital in March 2001 after developing pneumonia.

Anxious review

During the trial, the prosecution had claimed Rebecca's pneumonia had been a direct result of blood loss and shock that she suffered following an alleged sexual assault at the hands of one or other of her grandparents.

Prosecuting barrister, Toby Hedworth QC, said that having "anxiously" reviewed the state of the evidence and testimony which was yet to come, a decision had been made to offer no further evidence against the couple.

The lawyer said the prosecution came to their decision following the evidence of locum GP Dr Mary Donnelly and that of the state pathologist for Northern Ireland, Professor Jack Crane.

Dr Donnelly admitted for the first time, 11 years after examining the profoundly disabled child, that two of her fingers "unintentionally" slipped inside her.

Professor Crane said that he could not be sure that the laceration had led to the pneumonia which killed Rebecca.

'Human tragedy'

The judge described the case as a 'great human tragedy'

On Monday afternoon, the judge Mr Justice McLaughlin directed the jury of seven men and five women to find both Mr and Mrs Johnston not guilty and told them they were free to go.

The judge described the case as a 'great human tragedy'.

He said that as a result of the case Mr and Mrs Johnston, who are both in their 80s, had been attacked in their home and put out of their house.

Following the decision, Mr Johnston told the judge "thank you very much".

The teenager used a specially designed wheelchair and could neither walk, talk nor eat for herself.