Geraldine Azimkar – whose sapper son Patrick, 21, was gunned down with Mark Quinsey, 23, outside Massereene Army barracks in Antrim – reacted after the Court of Appeal in Belfast ruled the verdicts in the non-jury trial of Brian Shivers were unsafe and quashed his 25-year sentence.
Speaking from her home in London, she said the decision had left her and Patrick's father Mehmet Azimkar disillusioned with the criminal justice system.
High-profile republican Colin Duffy, from Lurgan, Co Armagh, was acquitted of the murder charges at the trial at Antrim Crown Court last year.
"It seems scandalous really that this terrible murder happened and the attempted murders happened and it looks like no-one is going to be held to account for it," Mrs Azimkar said. "We feel very let down by the criminal justice system. It does not seem to work for the victims of crime."
Shivers's appeal against additional convictions on six counts of attempted murder and one of possession of two firearms and ammunition with intent to endanger life, was also allowed by the Court of Appeal.
The Public Prosecution Service must consider whether to apply for a retrial for the 47-year-old, from Magherafelt, who is terminally ill with cystic fibrosis. He will remain in custody pending the decision.
Sappers Quinsey and Azimkar were gunned down at the gates of the barracks as they stepped outside to collect a pizza delivery in March 2009. The Real IRA claimed responsibility.