Austin Stack has interrupted a press conference held by Gerry Adams to accuse him of being a liar.
He says the Sinn Féin leader has information about who killed his father – Brian Stack – but won't reveal it to the guards.
The Portlaoise Prison officer was fatally shot by the IRA in the 1980s.
Speaking at the Davenport Hotel in Dublin earlier Mr Adams 'rejected absolutely' any allegations that he hadn't been honest.
