A lawyer for the family of murdered GAA official Sean Brown told a court in Belfast that a public inquiry could shine a spotlight on the truth about what happened.
Barrister Des Fahy said the fact that the truth remains hidden almost 28 years after the killing should be a source of "profound shame and embarrassment for the British state".
The British government today mounted a legal challenge to a decision by a judge last month to order a public inquiry into the 1997 murder by loyalist paramilitaries.
The challenge was heard before three judges at the Court of Appeal in Belfast.
Mr Brown was shot six times after being abducted as he locked the gates of Bellaghy Wolfe Tones GAA club in May 1997.
His widow Bridie and family were accompanied to the court by Sinn Féin deputy leader Michelle O'Neill and SDLP leader Claire Hanna as well as more than 40 supporters.
A lawyer for Northern Ireland Secretary of State Hilary Benn told the court the judge who ordered a public inquiry had acted "well outside his legal remit".
Barrister Tony McGleenan told the court that a decision about whether a public inquiry should be held was "for ministers to make and not the courts".
The British Government insists that the Independent Commission for Reconciliation and Information Recovery (ICRIR) can conduct a public inquiry style investigation.
Mr Brown's family do not accept that is the case and have refused to engage with the Commission.
Mr McGleenan told the court that no judge in Northern Ireland had ever before ordered a public inquiry and suggested that this demonstrated that it was inappropriate for the court to do so.
Northern Ireland's most senior judge, Lord Chief Justice Siobhan Keegan, pointed out that in February last year a coroner hearing an inquest into Mr Brown's murder also recommended that a public inquiry, and that call was supported by the Chief Constable of the PSNI.
That inquest revealed that police intelligence had linked more than 25 people to the murder, including a number of state agents.
No one has ever been convicted in connection with the murder.
Mr McGleenan maintained that the judge had made an error in law and exceeded his legal remit in ordering an inquiry.
He said the Secretary of State believes that as the ICRIR is already operational would provide the answers more quickly.
Repeated delays not beneffiting Brown's family
At one point one of the other judges, Mr Justice Treacy, asked Mr McGleenan who had benefitted from repeated delays in dealing with the case.
"It's certainly not Bridie Brown and her family," he said.
The judge added that it could be said that the state had benefitted from the delays.
The lawyer for the Brown family argued that Ms Benn is behaving unlawfully by failing to convene a public inquiry.
Des Fahy said an inquiry was the appropriate way forward as there had been no effective investigation into the murder.
"The murder of Sean Brown is an indelible stain on the body politic of this state," he said.
He told the three judges that today was the 57th time Mrs Brown and her family had been in court seeking the truth about the murder.
Mr Fahy said the judge's order for an inquiry to be held was "absolutely permissible".
He said a public inquiry "was and is the only option lawfully available".
The lawyer also told the court: "Instead of spending many years of happy retirement with her husband, Bridie Brown has spent the past 28 years in these courts searching for answers and the truth."
At the end of the hearing the presiding judge, Lord Chief Justice Siobhan Keegan, said the court would deliver its judgment, in what she described as a very complex case, as soon as possible.
