The gardaí and the PSNI have been criticised at the Smithwick Tribunal for failing to disclose investigations into allegations of garda collusion with the IRA in Donegal in 1991.
Judge Smithwick said the reports into the allegations should have been disclosed to the tribunal at the very start.
Instead they have only emerged as a result of information given by a retired RUC witness.
Former Garda Commissioner Noel Conroy carried out the investigation in the south.
Today he was called back to the tribunal and was questioned about why he never disclosed this investigation to Judge Smithwick when he gave evidence on a previous occasion.
In the conclusion of his report into alleged leaks of information to the IRA, Mr Conroy said he was unable to establish how the garda documents ended up in the hands of the IRA.
He told the tribunal today that he interviewed 240 people, including members of the force, although he did not question them as suspects for the leak.
Mr Conroy said he was stonewalled during his investigation and unable to come to a conclusion.
However retired RUC Witness 68, in his investigation into the same leak, said he was absolutely certain there was a leak to the IRA from several stations.
Mr Conroy said he was never told this by the RUC.
He also said he did not tell the Morris Tribunal about his report because he did not believe it was relevant to the tribunal, which was set up to investigate allegations of garda malpractice in Donegal.
Asked why he did not tell the Smithwick Tribunal about it, Mr Conroy said he was not asked anything about it but he insisted he was being as open as possible.
The witness was questioned at length about not informing the tribunal of the investigation but he insisted he was not trying to hide it.
Counsel for the PSNI, Mark Robinson, said Mr Conroy's stance was "simply outrageous".
However, Jim O'Callaghan, counsel for Owen Corrigan who is one of the three former gardaí being investigated by Judge Smithwick to see if he colluded with the IRA, pointed out that the PSNI had their report into the matter and they failed to disclose it to the tribunal.
This led to an exchange between the Judge and Mr Robinson with the Judge saying that the report was not given until the tribunal became aware of it and asked for it.
Instead the PSNI should have volunteered it and they did not.
Mr Robinson argued that people had retired and they were not aware of the report either, but when it was asked for they produced it.
Counsel for the tribunal, Mary Laverty, pointed out that both the Garda and the PSNI had sworn affidavits that the information already disclosed to Judge Smithwick represented everything they had about the issue of collusion.
Now it emerged that was not the case and they were left wondering what else had not been disclosed.
The allegations of collusion relate to the death of suspected UVF member Ian Spoule on 13 April 1991.
He was shot by the IRA, which claimed that he was involved in a bombing campaign in Donegal.
To prove this the IRA produced a copy of a garda record, a Fogra Tora, to a reporter showing that Spoule was wanted for questioning about the attacks.
A second man, Glen Monteith, who was also identified in the record, escaped a shooting attempt by the IRA on the same day.
The RUC contacted the gardaí and on 19 April then Chief Supt Noel Conroy was sent to investigate the allegations.
However, the day before the IRA announced they did not get the report from the gardaí but from a store of information in Spoule's house.
The Fogra Tora is not only circulated among garda stations but also to other police forces including the then RUC.
The Smithwick Tribunal is investigating claims that a garda passed information to the IRA which allowed them kill two senior RUC officers in March 1989 after leaving a meeting in Dundalk Garda Station.