A solicitor representing the families of five people killed at a shooting in a Belfast bookmakers in 1992, has said that the families believe that "dark forces" were working to keep information about the killings from the Police Ombudsman.
Niall Murphy was speaking after it was revealed that the PSNI failed to disclose "significant, sensitive information" about the Sean Graham bookmakers shooting to the Police Ombudsman.
Five people were shot dead at the bookmakers on the Lower Ormeau Road in an attack by a UFF death squad.
Ombudsman Dr Michael Maguire had been due to publish his investigation into the shooting in the coming months, but this is now expected to be delayed.
The new evidence's existence came to light when police prepared to disclose it to the bereaved families as part of civil proceedings.
The ombudsman's office said the material in question had opened new lines of inquiry in its investigation into the bookies massacre in which five people died.
The families feel that 20 years after the Good Friday Agreement there are unfortunately dark forces who are trying to undermine the Police Ombudsman's office. Niall Murphy
The PSNI has insisted it hadn't withheld the information deliberately and put the omission down to human error.
However, Mr Murphy told BBC Radio Ulster's Nolan Show that the families did not accept that it had been a mistake.
He said that the new evidence filled 30 lever arch files which could feature over 13,000 pages.
"Regrettably they fear that this is actually a policy which is designed to ensure that Dr Maguire does not publish his report, he has only five months left of his statutory tender that cannot be extended beyond July," he said.
"To be told that previous promises that were given in good faith by Dr Maguire cannot now be honoured is devastating.
"The families feel that 20 years after the Good Friday Agreement there are unfortunately dark forces who are trying to undermine the Police Ombudsman's office."
When it was pointed out that police had brought the evidence forward eventually Mr Murphy said that this did not absolve them of blame.
"Another analysis might be that they have achieved their ambition that Dr Maguire will not publish another report," he said.
"The circumstances that give rise to this bare to be considered more closely, (police) have legal obligations, they are not simply duties that he is attempting to fulfill. They are duties that must be fulfilled and are imposed on every Chief Constable in this jurisdiction."
Mr Murphy, of KRW law, said that he believed the new evidence may relate to the importation of guns from South Africa, which were also used in the Loughinisland massacre.
"We know from the Loughinisland report published in 2016 that there was a covert policing operation with regards to this importation from South Africa," the Belfast based solicitor said.
"We suspect that the material that has been withheld from the Police Ombudsman relates to that covert policing operation around this importation.
"These VZ-58 weapons had never been in this jurisdiction before ever. They would then go on to kill over 70 people. The arms importation that had Browning handguns, grenades, rocket propelled launchers would go on to kill 229 people.
"This is the most serious of issues, this is not civil disclosure in a row in a police station. This is the most serious of allegations that can be made. This material was withheld from an oversight body that was incepted to give confidence in policing."
Mr Murphy suggested that the information may not have been revealed if not for the civil litigation proceedings.
"When I advised the Police Ombudman's investigators to ensure that they had access to all of that information, the Ombudmsan told the families he was satisfied he had seen everything that was relevant, it appeared that it wasn't and that there was sensitive material that does give rise to further leads for investigation that had not been disclosed. That's a disgrace."
PSNI never sought to deliberately withhold this information from PONI and we deeply regret that the researchers responding to the PONI request were unable to find and disclose it. PSNI Deputy Chief Constable Stephen Martin
Mr Murphy said that he believed the new leads would be followed up but that it was "regrettable" that the information took "so many years" to come to light.
"Cockup or conspiracy? Either are not good enough. This information was known to both the Police Ombudsman and senior command of the PSNI before Christmas, this should have been a matter discussed at the policing board last week," he said.
Mr Murphy called for an urgent meeting of the Policing Board to be held to discuss the issue.
He said that the Irish Government should attend as co-guarantors of the Good Friday Agreement "to ensure that they are satisfied that the mistakes that have happened satisfy their obligations as co guarantors of our police process".
In a statement on Wednesday the PSNI acknowledged the mistake and offered to give ombudsman investigators "full and unfettered access" to police legacy systems.
Deputy Chief Constable Stephen Martin apologised to the families affected and said police were "deeply and sincerely sorry".
“PSNI never sought to deliberately withhold this information from PONI (Police Ombudsman Northern Ireland) and we deeply regret that the researchers responding to the PONI request were unable to find and disclose it," he said.
"This error became apparent when, in line with our commitment to maximum transparency, a different researcher working elsewhere in the PSNI found the material while preparing for disclosure in response to civil litigation.
“The fact that one part of the organisation was able to find the information while the other did not is a result of a number of issues including the differing levels of experience and knowledge of our researchers, the sheer volume of the material involved and the limitations of the archaic IT systems."