Sinn Féin TD Darren O’Rourke said he understood Mr Adams spoke to the party member after Detective Inspector Pat Marry went to the former leader for help.
Mr O’Rourke denied there was a culture of fear in the party, adding that he understood members do not need to consult senior members before giving information to gardaí or the PSNI.
The Irish Times reported on Tuesday that the unnamed Sinn Féin member gave a statement detailing how he heard Aaron Brady confess to the murder of Detective Garda Adrian Donohoe during the robbery of Lordship Credit Union in Bellurgan on January 25th 2013.
Mr Marry told the newspaper he had to go to a Sinn Féin TD for help before the witness was told by the party that there were no issues in him providing information about the killing.
Brady, a 29-year-old from Co Armagh, was convicted of capital murder at Dublin’s Central Criminal Court last week.
Mr O’Rourke said: “I don’t know that person, and again I don’t know the decision-making process in terms of their own thinking and why they felt they needed to do that.
“The party has been very clear that in so many cases and so many incidents, that people should come and make statements and bring information they have to the guards and PSNI.
“In fairness I don’t think the party presumed they needed to, you don’t need to come to Sinn Féin first before you do that, it’s clearly not the case.
“I think in how that developed and played out it was clear that the party don’t require that from people, and a very helpful and useful role was played by that person, which was the important point.”
Asked if the TD involved was Mr Adams, Mr O’Rourke said: “It’s my understanding that it was.”
He insisted there is no culture of fear in the party, adding: “I can say that as somebody who has been a member of this party for over 20 years and come into it without a strong republican background. I have never experienced that and the leadership has always been encouraging in terms of our important role as citizens first.
“I don’t know what the rationale was on behalf of that person, maybe it was them being over-cautious or second guessing themselves.”
Fine Gael TD Neale Richmond said the incident raises “serious questions”.
He added: “Once again when it comes to Sinn Féin and the law of the land, we have seen a shadowy parallel system at work.
“We have seen it in respect of the murder of Paul Quinn, the horrific treatment of Máiría Cahill, and at various repeated junctures.
“The revelation that a key witness in the murder of Detective Garda Adrian Donohoe wouldn’t speak with investigating gardaí until they cleared it with party figures raises serious questions that the party must answer.
“Why does a Sinn Féin activist feel they need to speak with party officials before making a statement to the gardaí? Do Sinn Féin believe their authority comes before that of the state? Will Sinn Féin encourage all who have information on the murder of Detective Garda Donohoe to present themselves to the gardaí?”
