Hazel Stewart's legal aid bill has spiralled to almost £630,000, the Belfast Telegraph can reveal.
It includes an extraordinary half-a-million pounds of taxpayers' money spent on her failed attempt to appeal her convictions for murdering her first husband and her lover's wife.
The former Sunday School teacher from Coleraine was jailed in 2011 for the double murder she helped to commit 20 years earlier.
In June she failed in a final challenge to one of her two murder convictions - leaving an enormous legal bill to be picked up by the public purse.
The Criminal Cases Review Commission, which investigates miscarriage of justice claims, has refused to refer her case to the Court of Appeal.
However, she could continue her appeal to the top European court - a move that could push her bill above £1m.
The Belfast Telegraph can reveal that as well as costing the taxpayer £15,433 for her defence throughout Magistrates Court proceedings, her defence in Crown Court proceedings cost a further £99,083.
Then came the huge £513,030 bill for Court of Appeal proceedings.
The costs were slammed by DUP MLA Edwin Poots. He said: "I think most people will be wide-mouthed and incredulous that half-a-million pounds was spent on attempting to lodge an appeal that most of us would have recognised was going nowhere from the outset, given the findings of the original case.
"Frankly, I think legal aid is given out far too easily for no-hope cases.
"It damages the credibility of legal aid, and often, as opposed to helping achieve justice and ensure justice is done, it prolongs the pain and agony of the relatives of the victims of murder and the victims of other crimes."
The figures were revealed by Justice Minister Claire Sugden in a letter shared with the Belfast Telegraph. It can also be revealed that while the National Crime Agency is seeking a recovery order in respect of Stewart's interest in residential property obtained as a result of her criminality, it is not seeking to recover money paid to her from her murdered husband's pension.
Stewart had been receiving Trevor Buchanan's police pension for an estimated 16 years.
Before her conviction she was living in a swanky property with her second husband, retired police Chief Superintendent David Stewart. In June it was reported that the NCA was seeking an order that Stewart must repay money gained following the death of Mr Buchanan (32).
At that stage Stewart was seeking even more legal aid to reclaim police pension benefits inherited from her murdered husband.
However, the letter from Ms Sugden suggests the NCA is no longer pursuing Stewart over the pension. "I understand the National Crime Agency, through its ongoing civil recovery proceedings, are seeking a Recovery Order in respect of the interest in residential property obtained by Hazel Stewart as a result of her criminality," Ms Sugden writes in the letter, dated August 22, 2016.
"The NCA inform me that they are not seeking to recover monies received through the police pension."
The NCA said: "The NCA has no comment to make on this at this stage."
Previously Arleen Elliott, the former president of the Law Society - which represents solicitors - gave a defence of legal aid in a Belfast Telegraph interview.
She said: "All of us uphold the principle that you are innocent until proven guilty and that is regardless of the person or the crime they are accused of.
"If defendants are not represented across the board it would actually break down the integrity of the system, resulting in unsafe judgments and public mistrust about judgments delivered by a court.
"You simply could not have it."
Stewart (53) is serving a minimum 18-year jail sentence in Hydebank for murdering Constable Buchanan and 31-year-old Lesley Howell, the wife of her then-lover Colin Howell.
She was unanimously convicted of both killings by a jury at Coleraine Crown Court in March 2011 after Howell confessed to the murders, and testified against her.
The pair's victims were found in a fume-filled garage in Castlerock, Co Londonderry, back in May 1991.
Howell pleaded guilty to the murders in 2010 and was ordered to serve at least 21 years behind bars.