An expert report on the Omagh bombing handed to the British and Irish governments more than a year ago contained damning evidence of security blunders that allowed the perpetrators to both carry out the atrocity and get away with it, victims' families have claimed.
Frustrated at the time it had taken for the authorities in London and Dublin to respond to the alleged failings outlined by the independent security specialists who wrote the document, last month relatives published part of it.
They withheld the majority of the papers, insisting they contained information too sensitive for public consumption.
One of the most significant sections, the families claim, were files of 4,000 emails detailing communication between an FBI agent, who had infiltrated the Real IRA at the time of the bombing, and his handlers.
While emails from agent David Rupert, who was apparently working in conjunction with MI5, have already featured heavily in past court proceedings, the relatives insist a number which indicated that a bombing was planned have never been made public.
They contend that the messages identify Omagh as a potential target and establish a time frame consistent with the eventual attack.
The families claim the information was not acted on or shared with Royal Ulster Constabulary (RUC) police officers working in the Omagh area at the time.
They say the report also contains evidence that an active intelligence operation was on-going on the day of the attack.
While it has previously emerged that intelligence operators were monitoring mobile phone communications on the day - claims levelled in a BBC Panorama investigation - a review by Intelligence Services commissioner Sir Peter Gibson in 2009 found that this surveillance was not in real time, and therefore could not have been used to prevent the bombing.
In 2001, then Northern Ireland Police ombudsman Nuala O'Loan published a hard hitting report criticising the RUC's overall handling of the police investigation into the crime.
After the 2006 trial of south Armagh electrician Sean Hoey, who was acquitted of the murders, a judge castigated the way police had handled vital pieces of evidence.