The security services have been accused of not acting on information in a number of high profile cases over the years, including the 1998 Omagh bomb, the single biggest atrocity of the Troubles.
In a report published in 2014, the Police Ombudsman said failure to disseminate data detracted vital resources from the initial investigation into the bombing which killed 29 people, including a woman pregnant with twins.
Police Ombudsman Dr Michael Maguire said the RUC Special Branch had not provided all intelligence because of their interpretation of the law at that time.
While he found no evidence that police had information which, if acted upon, could have prevented the Omagh bombing, the Ombudsman concluded that Special Branch had acted "cautiously" in not disclosing all the intelligence available to the investigating team.
Almost a decade earlier, the murder of Pat Finucane also led to questions over the role of police and led to security chiefs being accused of failing to warn the Belfast solicitor of impending death threats.
A 2004 report into the 1989 murder and published by retired Canadian judge Peter Cory revealed that members of the security forces had repeatedly failed to inform the father-of-three that his life was in danger in the10 years before his death.
The report also revealed how the RUC and MI5 had prior knowledge of three previous loyalist plots to murder Mr Finucane but did not share that knowledge with him.
There have also been persistent claims that the 1981 murder of Rev Robert Bradford could have been prevented and that RUC Special Branch and Army Intelligence had knowledge of his fatal shooting three days before it happened.
The 40 year-old Ulster Unionist MP for South Belfast and father-of-one died instantly along with caretaker, 29-year-old Kenneth Campbell, after being targeted by the IRA at a community centre at Benmore Drive in Finaghy in 1981.
Claims made in journalist Greg Harkin's 'The Special Branch Files' detailed how a botched undercover operation led to the death of the MP who was "sacrificed" to protect agents within the ranks of the IRA.
In another Police Ombudsman report in 2014, Dr Michael Maguire found the murder of Sergeant Joe Campbell - shot on February 25, 1977, as he locked the main gates of the Cushendall Police Station - "could have been prevented".
Dr Maguire said senior police officers within the RUC command structure were "aware of a specific threat to one of their officers" but failed to warn him about it and did not pass the information to detectives investigating his murder.
On what was the last day in office of former PSNI chief Matt Baggott, the damning 50-page report found his predecessors could have prevented Sgt Campbell's murder and that "senior RUC officers and management had "information on a very specific threat and failed to respond."
In addition, it was highly likely, he said, that the intelligence threat against Sgt Campbell was known all the way up to the then chief constable, Sir Kenneth Newman.
Police also stand accused of withholding vital information about an IRA booby trap bomb which exploded in a property in the Creggan Estate, Derry, in August,1988.
The device, which killed three people at the scene and a third seven months later, was triggered when three concerned neighbours entered the flat of their friend who hadn't been seen for several days.
The Ombudsman said that while police in Derry faced "enormous pressures" at the time, in this instance officers did not fulfil their duty to protect the public.
