The Taoiseach, Mr Ahern, has said he had no evidence to prove that Ray Burke was corrupt before he appointed him to his first Cabinet in 1997.
Mr Ahern is set to face renewed opposition pressure in the Dáil today over his appointment of Burke to the prestigious post of minister for foreign affairs when he became Taoiseach.
In his first public comment since Burke received a six-month prison sentence for tax offences, Mr Ahern said he had always maintained that "the law is the law and it must be applied to everybody".
He was aware of the allegations surrounding Burke and had investigated them "so far as I could". However, the Taoiseach said he was obliged to take into account only the information he had to hand about Burke when he gave him the foreign affairs portfolio.
"I investigated so far as I could and I had to go on what evidence I had. And at that stage, he was a minister that I required to do a certain job. I did not have evidence against him," he said.
Burke's conviction has revived the controversy surrounding that appointment, with the opposition claiming it reflected badly on the Taoiseach's judgment and some Fianna Fáil TDs saying in private that the decision was unwise.
They have maintained that the appointment has created avoidable damage for Mr Ahern and the party.
The official spokesman for Mr Enda Kenny, said last night that the Fine Gael leader will question the Taoiseach about the appointment when the Dáil reconvenes today.
Mr Kenny has said the Taoiseach has questions to answer about the appointment because he was close to Burke, described him as an "honourable man" and appointed him to a very sensitive post in his first cabinet.
While Mr Ahern made no immediate comment when Burke was sentenced, he told RTÉ yesterday that he had said several times before that he would never have appointed him to the cabinet if he known what the planning tribunal later uncovered.
"Of course, hindsight is great. I'm on the Dáil record several times saying if I had have known that Ray Burke was going to get the kind of report that he got from the tribunal, of course, I wouldn't have appointed him," he said.
Politics was about public service and serving the public interest.
"And when you breach that - we've tough laws in this country - you have to deal with them."
While he knew about the "issues" that were raised about Burke at the time, he suggested that he did not have resources required in the short time before he formed his first cabinet to investigate them fully.
"Of course, now it's easy looking back to say that if we had only known 1 per cent of these things. But seven or eight years on, I didn't have in the short few days, weeks, the kind of resources to do this, but that's been dealt with now."
Mr Ahern said he was conscious that Burke's imprisonment was a "huge tragedy" for him and his family.
Separately, the Minister for Defence, Mr O'Dea, said that any person thinking of evading tax in the future would be deterred by Burke's imprisonment.
He had sympathy with Burke because his financial situation had been ruined and his reputation destroyed.
The public should remember that Burke had a wife and a family who were innocent victims, he said.
