The former Fine Gael Senator and TD went against the advice of the county manager in 1992 and supported a motion to rezone agricultural land in Carrickmines, owned by Jackson Way.
Frank Dunlop claims the councillor was bribed for his vote, but Mr Cosgrave said it was a lie.
That motion was defeated and further attempts to rezone the land were made in 1997.
Once more, officials advised against it as there was no road network to support development and no water supply.
However, this time the motion was passed and part of the land was rezoned.
Mr Dunlop claims Cllr Cosgrave asked for and got £5,000 for his support. The councillor says this claim was a lie, and that Frank Dunlop invented the bribes and some of the meetings.
After rezoning, the land would have increased in value and the local authority would have had to pay more if it needed to buy the land for a new motorway. However, Cllr Cosgrave said he did not see anything wrong with this, and that there was cost factor in everything.
He said developing the area might bring in more rates and employment, and that one had to look at the bigger picture.
Mr Cosgrave said his vote was never bought and that he did not feel compromised because he had taken thousands of pounds in political donations from Mr Dunlop.
He said the bottom line was whether the Flood Tribunal believed him or Frank Dunlop.
