The Fianna Fáil leader says Gerry Adams is not telling the truth about the murder of Brian Stack.
The Portlaoise Prison officer was fatally shot by the IRA in the 1980s.
Speaking in the Dáil yesterday - the Sinn Fein leader reiterated that Mr Stacks son Austin gave him the names of four men who may have information on the case - something the Stack family denies.
Fianna Fáil leader Michael Martin says Mr Adams statement doesn't go far enough: "I'm very clear that the leader of Sinn Fein has knowledge of people who can be of great assistance to the Gardaí, on this case.
"If he genuinely wants to bring people to justice for the murder of Brian Stack well in my view he is not prepared to do that.
"Lets be very clear, he endeavoured to wrap the peace process around his refusal to do this, that is not good enough because in no way can the murder of Brian Stack be justified."