The parents of murdered Catholic schoolboy Thomas Devlin, who battled for almost three years to have their son's killers charged, have said the North's Public Prosecution Service (PPS) is now even less accountable than when they waged their campaign for justice.

Penny Holloway and Jim Devlin told the Sunday Tribune that, far from reforming, the PPS appeared to have learned no lessons from its "total and spectacular failure of duty" in their son's case.

Thomas Devlin (15) was stabbed to death in August 2005 as he walked home in north Belfast with two friends.

The PPS twice refused to prosecute Nigel Brown and Gary Taylor. who were convicted of Thomas's murder in February. A jury took just 80 minutes to reach the verdict.

The PPS had initially stated that the available evidence meant there wasn't a reasonable prospect of conviction. The prosecution went ahead only after the Devlins insisted on independent advice from counsel in England who stated there was "compelling circumstantial evidence" against both men.

PPS senior assistant director Raymond Kitson, who conducted an internal review in 2008 which upheld the original decision not to prosecute, was granted a CBE in the Queen's birthday honours' list last week.

"Raymond Kitson has been rewarded for his lengthy service to the civil service and the PPS but, in our view, his CBE is not for his service to victims like Thomas and us," said Penny Holloway.

She called for a "complete overhaul" of the PPS led by criminal justice experts from outside Northern Ireland.

In a statement to the Sunday Tribune, the PPS apologised for "any additional stress" the Devlins experienced during the review of the original decision not to prosecute.

It said it had previously met the family and hoped to do so again soon.