PSNI is criticized for failing to disclose to the ombudsman of the police "sensitive and important information" about a loyalist massacre.
Sinn Fein said last night that he wanted an urgent meeting with police chief George Hamilton to discuss the "appalling and unacceptable" failure of the force.
Groups of victims also attacked the PSNI, which apologized for its actions.
The Ombudsman, Michael Maguire, has asked the Ministry of Justice to conduct an independent review of how the police divulge information.
The campaign group "Families for Justice" said that this "should start urgently".
The Police Ombudsman revealed that the PSNI had not disclosed any information, in part relating to secret police operations, to its investigators working on the 1992 UFF massacre in Sean Graham's Belfast Ormeau bookstores. Road, Belfast.
Dr. Maguire stated that the existence of these documents had been brought to light when the police were prepared to reveal it to the families of the victims, in the course of a civil proceeding.
PSNI insisted that it did not deliberately conceal this information and attributed this omission to human error.
The Ombudsman's office said the documents in question had opened new lines of inquiry as part of its investigation into the bookmaker massacre that had killed five people.
He also did the same with respect to various homicides perpetrated by loyalists in the northwest between 1988 and 1994, as well as the Ombudsman's investigation into the 1993 assassination, the Teenager Damien Walsh, in a coal depot in the west of Belfast.
The reports describing the findings of these surveys, which were to be published in the coming weeks, will now be delayed.
Last night, PSNI proposed giving Ombudsman investigators "full and unhindered access" to legacy police systems. A spokesman for the ombudsman's office praised this decision.
In a statement released yesterday, Dr. Maguire said, "My staff learned that the police were preparing to release various documents in the context of an impending civil proceeding.
"Following a request from this office, the police provided us with these documents, which allowed us to identify important and relevant evidence for a number of our investigations.
Subsequently, the police also identified a computer system that they felt had not been properly searched when responding to previous requests for information.
"In this case, it would appear that information that the police told us they did not exist has now been found."
Dr. Maguire said that effective disclosure of information was essential to dealing with the past.
"The public must be certain that, when asked, the police provide all the relevant information that they have about certain cases," he said. "The police told us that the problems resulted from a combination of human errors resulting from a lack of knowledge and experience and the complex challenges associated with the bulky matter – bits and pieces of 44 million paper and microfilm records – which is stored at various locations and on a range of archaic media and computer systems. "
Dr. Maguire added: "In the interest of public confidence in the maintenance of order, I contacted the Department of Justice to request that an independent review be conducted methods used by the police to disclose information ".
It is understood that the material has implications for up to 30 murders.
Gerry Kelly, Sinn Fein MP, said: "The revelations that the police failed to reveal vital information to the police ombudsman's investigations into dozens of murders committed by loyalist death squads are frightful and unacceptable.
"Many people will see this as further proof that the hiding of the role of the British state forces in the conflict in Ireland is systemic.
"The PSNI can claim that this is a mistake, but how long did it take after the PSNI hierarchy became aware of this failure before informing the police mediator or affected families? ? "
Mr. Kelly stated that his party would request an urgent meeting with George Hamilton and would also raise the matter in front of the police commission.
"The PSNI or the British government should not be excused, trust in the police is at its lowest level in many years, and immediate action is needed," he added.
Baroness Nuala O. Loan, a former police mediator, told Belfast Telegraph that her heart was family oriented.
"They have been fighting for so long to try to understand what has happened and now," she said.
"The PSNI has had decades to put order in its records and this has not been done yet.
"The question must be what else is where they found this material, how many other cases are affected, how did it go?"
Baroness O. Loan continued: "What the police chief needs to do now, is do what was supposed to be done years ago – publish all the special branch records and other documents in accordance with the law.
"Those who have suffered during years of unrest and who are still suffering deserve the truth, not broken promises, not manual errors, not hesitations.
"The future of law enforcement must not include continuous failures of this magnitude.
"It does not have to be like that, it's awful."
The director of the Justice Administration Commission, Brian Gormally, said that the statement of human error committed by the PSNI "simply insults our intelligence".