Northern Ireland's former deputy Director of Public Prosecutions was asked to stay at home over a decision not to prosecute Freddie Scappaticci for perjury.
No wrongdoing is alleged against Pamela Atchison.
It has been widely reported that Mr Scappaticci was the British spy in the IRA known as Stakeknife, whose activities are under investigation in connection with many murders during the Troubles.
Mr Scappaticci swore an affidavit to Belfast's High Court to say he was not the mole.
The Public Prosecution Service (PPS) decided not to prosecute him for perjury because he was in fear of his life, the BBC’s Panorama programme said.
It added a senior DPP lawyer involved in the decision not to prosecute Mr Scappaticci for perjury was Ms Atchison, who went on to become Northern Ireland’s deputy Director of Public Prosecutions.
After the current director Barra McGrory QC decided to review the decision, Ms Atchison was asked to stay at home last year. She has since retired.
In 2015 Mr McGrory said he had serious concerns about the decision.
He added: “Having reviewed all of the available evidence, I consider that the original decision did not take into account relevant considerations and also took into account irrelevant factors.”