The Public Prosecution Service has a two step test for prosecution. First, they consider whether or not the evidence which can be adduced in court is sufficient to provide a reasonable prospect of conviction. Secondly they consider if prosecution is required in the “public interest”.
Therefore there could be a case where, on the face of it,there is compelling evidence against X but the prosecution does not take place because it is not in the public interest. This includes “where details may be made public that could harm sources of information, international relations or national security”. [Sometimes referred to as the ‘Shawcross doctrine’]
It does not require a great leap of imagination to consider that members of Sinn Fein/IRA may already have benefitted from this second limb or may do so in the very near future.
What could be more in the public interest than the protection of “the peace process”?