Police in Omagh received four warnings of terrorist attacks before the bomb attack that killed 29 people, it was claimed last night.
Officers have admitted two threats - a telephone call and a tip-off by an informer - in the run-up to the atrocity.
But according to a Channel 4 News investigation, police in the Co Tyrone town got two more - one of them the day before the massive car bomb exploded on August 15th, 1998.
The programme claimed a detective who passed on the first warning to the RUC Special Branch 11 days before the "Real IRA" struck broke down and wept uncontrollably when he later claimed lack of action by colleagues.
An internal report said: "The officer has an overwhelming feeling of guilt, and at the outset asked 'Why has it taken two years for anyone to come and talk to me about this?'"
Even though police on both sides of the border carried out a massive investigation into the bombing, nobody has been charged in Northern Ireland. One man convicted of conspiring to cause an explosion at the time of Omagh was jailed in Dublin earlier this year.
A second man, alleged "Real IRA" boss Mr Michael McKevitt, from Dundalk, Co Louth, is charged with directing terrorism and due to stand trial next February.
The Police Service of Northern Ireland has begun a fresh criminal investigation in a bid to track down the bombers. Relatives of some of the dead have started legal action to sue the men they claim were responsible.
Gardaí are also investigating claims that one of its senior officers knew the "Real IRA" was planning a car bomb attack in Northern Ireland three weeks before Omagh but decided against passing the information to the RUC for fear of exposing an informer.
PA