The explosion killed 29 people and unborn twins in 1998
BBC Panorama reporter John Ware has told MPs a government investigation into the intelligence surrounding the Omagh bombing was defective.
Twenty-nine people were killed in the Real IRA atrocity.
A government review was set up after Panorama claimed GCHQ was listening to some of the mobile telephones used to coordinate the 1998 bombing.
Mr Ware told the Northern Ireland Affairs Committee the government's report was flawed.
He said the approach of its author Sir Peter Gibson was "adversarial", claiming he was "impatient and dismissive".
The BBC reporter stood by his programme and said Sir Peter's report had failed to tackle the nub of his programme.
The Panorama programme presented by Mr Ware, was entitled 'What the police were never told '.
Last week the committee met relatives at Stormont and family members want the government to set up a full public inquiry.
Wednesday's meeting with Mr Ware is expected to be followed by other evidence sessions in the weeks ahead.