The Smithwick Tribunal has heard that a garda identified as an IRA mole by a republican source was missing from duty on the night the source was abducted, interrogated and killed by the IRA.
However, the Tribunal also heard there was no evidence now retired Det Sgt Owen Corrigan was involved in the death of John McAnulty in July 1989.
The Tribunal is investigating allegations that information was passed from a garda in Dundalk to the IRA which led them to ambush and kill two senior RUC officers in March 1989 just minutes after leaving the garda station in the town.
Mr Corrigan, and former sergeants Leo Colton and Finbarr Hickey, all deny the allegation of collusion.
This afternoon the Tribunal heard more evidence from Witness Z, who worked as a detective in the RUC special branch based in Newry.
He said he was told by Mr McAnulty that Mr Corrigan was passing information to the IRA. Although not a member of the IRA, Mr McAnulty was involved with members at all levels according to the witness.
He told Michael Durack, counsel for the Garda Commissioner, that there was no other information he was aware of that backed up the claim against Mr Corrigan.
He said he really did not want to give evidence to the Tribunal but he did so "for the sake of justice and to get this out of my system."
It was also put to him that his superior officer did not give any credence to the allegation against Mr Corrigan and simply did not believe it.
Witness Z said that the officers he worked with all believed it.
Under cross examination by Jim O'Callaghan, counsel for Mr Corrigan, the witness said there was no evidence which linked his client to the murders of RUC Chief Supt Harry Breen and Supt Bob Buchanan.
He said he had decided to give evidence to the Tribunal after he was told by the solicitor for the Breen family, John McBurney, that Mr Corrigan was absent without leave from work on the night his source was killed by the IRA.
Counsel for the Tribunal, Mary Laverty, pointed out this was evidence already heard before the Tribunal from former Chief Supt John Nolan, who said that although Mr Corrigan was on duty the night of the murder, he could not be found anywhere.
Witness Z stated he was not saying Mr Corrigan was involved in the murder of Mr McAnulty but he just needed to give a reason as to where he actually was on the night.
Counsel for the former garda said he believed the intelligence form was rated C6, which meant the source might be reliable but this information was not really believable.
Mr O'Callaghan also told the Tribunal that his client, who was due to give evidence next week, was now ill and would not be able to attend.
Judge Smithwick adjourned the sittings until next Tuesday and said there were only two witnesses left to give evidence.