Pressure on Gerry Adams to provide Irish police with the name of an IRA man who may have information on the murder of Brian Stack has intensified.
Irish Labour Party leader Brendan Howlin said he believed Mr Adams was "committing crime" by refusing to hand over the name.
Meanwhile, Finance Minister Michael Noonan said "murder is murder" and anyone with information had an "obligation" to pass it on to the police
Mr Adams insists he doesn't know who killed prison officer Mr Stack more than 30 years ago.
He facilitated a 2013 meeting between Mr Stack's sons, Austin and Oliver, and an IRA member who looked into the killing.
He arranged to have them driven in a blacked-out van to meet the IRA member and Austin believes this man knows who killed his father.
Despite Mr Stack's demand that Mr Adams pass on his name to Garda, the Sinn Fein president last night reiterated that he had to protect his sources.
He told RTE this was "not to protect individuals involved" but to ensure when a "truth recovery process" was eventually set up, families could get "closure".
"I'm about the business of trying to make peace," he said.
Last night Mr Howlin said it was clear Mr Adams knew the identity of the IRA man who investigated Brian Stack's murder
"In possessing this information and refusing to reveal to police, I believe he is committing crime," he said.
Mr Noonan urged Mr Adams to give police the names of the van driver and IRA man from the 2013 meeting.
"Murder is murder", he said.
"Any person, whether they are a TD, or a councillor, or an ordinary citizen, has an obligation to give information to the Guards."
A Sinn Fein spokesman said Mr Adams had indicated that he would co-operate with Garda, but did not reply when asked if this included passing on the IRA man's name.
The spokesman said it was not an issue "politicians should be attempting to make political capital from".
Separately, a Dail committee is to examine whether Fine Gael TD Alan Farrell abused Dail privilege in naming Sinn Fein TDs Dessie Ellis and Martin Ferris as two of the individuals mentioned in an email sent by Mr Adams to the Garda Commissioner.
Mr Ellis and Mr Ferris both strenuously deny any involvement in Mr Stack's death.
Kerry TD Mr Ferris was the IRA commanding officer in Portlaoise during his time in prison for gunrunning.
In his authorised biography Mr Ferris is scathing about Mr Stack, and outlines the continual clashes between the authorities and IRA prisoners.
The Provisionals wanted their own command structure to control the prison. But the prison governor and his senior officers, led by Mr Stack, battled to maintain control.
"Stack was a particularly vindictive individual.
"He would never forget a previous incident, and if he took a dislike to a certain prisoner, he would wait until a suitable opportunity arose to punish the man in some way or other," Mr Ferris says in the book, which was published in 2005.