At least £40,000 has been wasted on a failed prosecution against a man accused of the Omagh bombing.
Seamus Daly walked free from court last month after the Public Prosecution Service withdrew the case.
Daly had been charged with murdering 29 people in the single biggest atrocity of the Troubles.
However, the case collapsed before it even reached trial amid concerns over the reliability of the prosecution's star witness.
The Belfast Telegraph has learned the costs incurred by the PPS have topped £40,000.
It does not include Daly's legal costs, which are likely to run to tens of thousands of pounds.
TUV leader Jim Allister said the public had been left to foot the bill for a case which delivered nothing.
"What concerns me most is that there was no return whatsoever on this expenditure," he said.
"Obviously £40,000 is a huge expenditure on just the start of a prosecution. If it had resulted in a trial and a conviction, it would have been money well spent.
"But it's hard to see that it was well spent when it resulted in no product whatsoever."
The Omagh bomb saw the single biggest loss of life in the history of the Troubles in Northern Ireland.
A dissident republican car bomb ripped through the Co Tyrone market town on the afternoon of August 15, 1998.
The death toll included nine children and three generations of the same family.
Daly, a 45-year-old bricklayer from Jonesborough, south Armagh, has always denied involvement in the bombing.
However, in April 2014, he was arrested and charged with 29 counts of murder.
He also faced charges of causing the explosion and possessing the bomb, and two charges relating to another bomb plot in Lisburn in April 1998.
However, five weeks ago the charges were withdrawn after the PPS decided there was no reasonable prospect of conviction.
In response to inquiries from this newspaper, the PPS said the cost of the prosecution was at least £40,157.
It includes fees paid to prosecuting counsel and witnesses' expenses.
The decision to pull the case was taken after star witness Dennis O'Connor gave inconsistent evidence and contradicted his previous testimony.
O'Connor, a builder from Kilkenny and a convicted fraudster, had told police he received a call from Daly around 20 minutes after the bomb went off, from a phone prosecutors said was used by the bombers.
But under cross-examination at a pre-trial hearing, O'Connor admitted the call may have been made a week earlier.
Mr Allister said the PPS should have tested the reliability of witnesses at an earlier stage.
"It is part of the prosecution's function to assess the value and credibility of your witnesses," he added.
"The question I would have in this case is why did they not realise it sooner."
Last month the PPS said the decision to withdraw the charges was taken "following a careful review of the current state of the evidence".
The PPS added: "Having conducted a careful review of the case with the prosecution team, the Director of Public Prosecutions Barra McGrory QC has concluded that the available evidence no longer provides a reasonable prospect of a conviction. Consequently the prosecution cannot be continued."
Seven years ago Daly was one of four men found liable for the attack in a landmark civil case taken by some of the bereaved families.
They were ordered to pay £1.6m in damages to relatives - money they are still pursuing.
However, no one has been convicted in a criminal court.
In 2007 south Armagh electrician Sean Hoey was found not guilty of the 29 murders after a marathon trial at Belfast Crown Court.