Dr Ray Byrne joined CIE in 1995 as director of programmes and projects when the group advertised for "six of the best" to fill vacancies in its top management.
A civil servant since 1974, with postgraduate qualifications in statistics, economics and public administration, his brief included the evaluation, implementation and management of large infrastructure investments at CIE's cash-starved bus and rail companies.
But on one occasion yesterday, he claimed his role was limited to securing EU and Exchequer funding for the companies. At the inquiry into a £36million overshoot on a 1997 rail signalling programme, Dr Byrne said he did not know the project was faltering with costs spiralling when he resigned his full-time post in July 1999.
The overrun and difficulties linked to the construction of a telecoms network on the railway for the Esat group were described by a British-based consultant to Iarnrod Eireann as "the cock-up of the century".
Yet despite evidence heard in earlier sessions of the inquiry that figures within Iarnrod Eireann had considered breaking its signalling contracts late in 1998, Dr Byrne claimed the warning bells were not ringing in mid-1999.
When his full-time position at CIE ended, he was immediately engaged as a part-time consultant to the group. While still working in that capacity, he was hired by Esat Telecom as a "strategic consultant".
Dr Byrne said he secured the job because of his public sector and transport experience. He informed Esat's chairman, Mr Denis O'Brien, that there could be no conflict of interest in his dual role.
The inquiry has heard that CIE prioritised work on the Esat project over its own signalling programme and that the provision of access to Iarnrod's railway breached its procurement policy. In addition, its chairman Mr Sean Doherty TD has said the Esat network proved to be a significant asset to the company when it was floated in 1997 and when sold to BT for $3.7 billion in 2000.
The most searching questions Dr Byrne faced yesterday centred on his role in the Mini-CTC signalling plan, which remains incomplete. While Dr Byrne displayed a thorough grasp of the internal structures in CIE and of EU funding programmes, his response to many questions was that he did not know or could not remember.
For example, Dr Byrne said he had once met the former minister for public enterprise, Mr Michael Lowry, but could not recall whether they had spoken by telephone.
Iarnrod Eireann's chief executive, Mr Joe Meagher, has said a capital monitoring group set up by Dr Byrne "effectively replaced the process of formal reports on capital projects to the CIE board which ceased in 1995". Dr Byrne said that was a "sweeping statement".
On claims by other witnesses that he cancelled each of the monitoring group's meetings in the first nine months of 1999, Dr Byrne said he was not sure that he had made all the cancellations.