The PSNI has been accused of trying to maintain an aura of garda collusion by being selective in its handling of information at the Smithwick Tribunal.
Jim O'Callaghan, counsel for former Det Sgt Owen Corrigan, told the tribunal today that information that could show the innocence of his client was not being allowed into the public domain by the PSNI.
Counsel for the former garda also said the PSNI had not asked Mr Corrigan when he was in the witness box if he had colluded with the IRA, because he said it did not actually believe it.
Mr O'Callaghan made his comments in a discussion over the grading attached to an RUC Special Branch intelligence form known as an SB50.
That form contained information from a south Armagh businessman and smuggler, John McAnulty, who told his RUC handlers that Mr Corrigan was passing information to the IRA.
Counsel for the former garda is arguing that the grading of the intelligence should formally be made public.
The forms were graded with a letter between A and F, which related to the reliability of the source, and with a number between one and six, which related to the intelligence.
It is believed that the form relating to Mr Corrigan is graded C6.
Retired RUC Supt David McConville told the tribunal at a previous hearing that the number did not mean the information was not believed, it just meant that it could not be verified.
Today, some of evidence from Mr McConville, which had been heard in private session, was read into the public record. The grading of the intelligence form had been redacted at the request of the PSNI.
Counsel for the Garda Commissioner, Michael Durack, supported the request by Mr O'Callaghan for the grading to be made public.
Mr Durack pointed out that this system had been abandoned by the RUC in the late 1990s and there was no issue of national security involved.
He said the tribunal was triggered to a significant degree by this document and the credibility attached to the information in it was important.
The judge will hear further legal arguments next week before giving his decision.
The Smithwick Tribunal was set up to investigate suggestions that a member of the gardaí passed intelligence to the IRA, which allowed them to ambush two senior RUC officers.
Chief Supt Harry Breen and Supt Bob Buchanan were killed just minutes after leaving a meeting in Dundalk Garda Station in March 1989.
Three former officers, Mr Corrigan, Sgt Leo Colton and Sgt Finbarr Hickey all deny the allegation that they colluded with the IRA.
