A Garda officer has told the civil case into the Omagh bombing that an empty underground room was found during a search of Liam Campbell's house in Co Louth in October 2000.
The entrance to the underground room was discovered by gardaí inside a cupboard.
The civil action is being taken by six families against five men they believe are responsible for the blast, which killed 29 people, including a woman pregnant with twins.
Michael McKevitt, Liam Campbell, Colm Murphy, Seamus McKenna and Seamus Daly all deny any involvement in the bomb attack in the Co Tyrone town on a busy Saturday afternoon in August 1998.
The court heard that gardaí found a number of items during the search of the house and adjoining shed including £2,000, three mobile phones, a walkie-talkie, a motorola radio and six aerials.
Mr Campbell is not legally represented in the case.
The court heard that a small container of mercury was found during a search of the home of another of the five defendants, Mr McKevitt, in 2000, along with photos, newspaper cuttings and a map of the former Yugoslavia.
Inspector William Hanrahan told the court that when interviewed, Mr McKevitt denied knowing the FBI agent David Rupert.
Earlier, surveillance officers who followed the movements of man accused of being responsible for the Omagh bombing today denied putting their heads together to make statements.
A barrister for Michael McKevitt also questioned the work practices of gardaí, who failed to keep any written notes or photographs of alleged meetings his client had with an FBI agent who infiltrated the group.
Kieran Vaughan QC told the court sitting in Dublin that it was obvious officers had memorised undated statements for the hearing, which were made after Mr McKevitt's arrest for terrorist offences in January 2001.
On day 19 of the case, which has heard four weeks of evidence in Belfast Crown Court, members of the Garda Surveillance Unit said they witnessed Mr McKevitt and David Rupert together at a Dundalk housing estate on 18 February, 2000.
The accuracy of testimonies given by Detective Garda Fergal O'Brien and Sergeant Seamus Lynch, who maintained they each saw the men in the cul-de-sac before and after a meeting in a house, were questioned by Mr Vaughan.
They told the District Court that at no time did any officer consider video recording or photographing the meeting, did not logged times or car registration numbers, or note the clothes the suspected terror boss was wearing.
Both gardaí said it was not their job, but the responsibility of their senior officer Detective Sergeant Thomas Finbarr Healey who gave evidence yesterday, to record the movements around Oaklands Park on the night.
Mr Vaughan claimed that reports and subsequent statements from all three were worded and phrased the same, and had not been dated, suggesting they were written together.
When asked if he had written the statement with his colleague Detective Garda O'Brien said he had never changed his evidence.
Asked the same question Sergeant Lynch said he made his statement alone and would not have been un touch with his colleagues on a regular basis at the time.
Earlier, a British judge made history when he temporarily presided in the Irish courtroom to hear submissions from counsel for the defendants.
