The Garda Commissioner's legal team has launched an unprecedented attack on the PSNI at the Smithwick Tribunal.

Diarmuid McGuinness accused the PSNI of failing the families of two murdered RUC officers, their colleagues in the Garda Síochána and the tribunal itself.

In his closing submission, Mr McGuinness launched his blistering attack on the conduct of the PSNI and their failure to cooperate on sharing intelligence.

It was the last day of hearings at the tribunal, which is investigating allegations of collusion between gardaí and the IRA in the murder of two RUC officers in March 1989.

Chief Supt Harry Breen and Supt Bob Buchanan died in an IRA ambush just minutes after leaving a meeting in Dundalk Garda Station.

Three former garda sergeants, Owen Corrigan, Leo Colton and Finbarr Hickey, have all appeared before the tribunal.

They all rejected the allegation they colluded with the IRA in the murders.

Counsel for the Garda Commissioner said the tribunal chairman had been presented with "a Niagara of intelligence which is said to exist" with Assistant Chief Constable Drew Harris swearing it all to be accurate.

However, he said the intelligence had been withheld from the tribunal without justification or cause.

"It is wholly exceptional and wholly inexplicable that they have not shared this intelligence," Mr McGuinness said.

"It beggars belief", he added, how the judge was to decide on this intelligence and also on the whole issue of collusion.

Counsel for the Garda Commissioner urged the judge to "ransack the dictionary for the harshest possible words to use in relation to them in frustrating the work of the tribunal".

In his submissions earlier, Mark Robinson, counsel for the PSNI, acknowledged that there would be some criticism of the fact that they had brought forward this intelligence, but had not been able to elaborate in more detail.

There were still those intent on killing and the information came from operations that were designed to save lives and as such it was difficult for the PSNI to produce the information.

Mr Robinson said if Mr Corrigan's claims were true that he had the best sources within PIRA, how did he not know about the ambush being planned to kill Chief Supt Breen and Supt Buchanan.

He also questioned the completeness of the internal garda investigations into allegations of collusion between gardaí and PIRA.

Counsel for Mr Corrigan, Jim O'Callaghan, argued that there was no evidence to support the claim that his client was involved in collusion.

He said that Supt Buchanan crossed into the Republic at least 39 times between August 1988 and his death in March 1989.

Concerns had been expressed about the frequency of his visits and regretfully he said the IRA victim was "careless".

It was his client's view that he was the victim of a conspiracy set up to deflect attention from cases of collusion in Northern Ireland, such as the murder of solicitor Pat Fincuane.

Neil Raferty, counsel for former British agent Peter Keeley who also uses the name Kevin Fulton, also made a submission.

His client worked undercover for the British security forces in the IRA and has been described as a "liar", "conman" and "fantasist" by several previous witnesses.

In his submission today, Mr Raferty said Mr Keeley had come before the tribunal to give evidence of what he knew.

Former Det Sgt Corrigan, he said, was a "disgrace to the uniform", was corrupt and did collude with the IRA.

The solicitor for the Breen family, John McBurney, praised the work of the tribunal in trying to establish the truth.

However, some obstacles had proved to be immovable or impenetrable, he said, despite the best efforts of the tribunal.

The tribunal was set up in 2005 and began its investigations the following year.

In June 2011, Judge Peter Smithwick started hearing evidence in public.

The tribunal has sat for over 130 days and heard from around 200 witnesses.