Many republicans and nationalists are "outraged" at how Robert McCartney's murder is being "cynically exploited to undermine republicanism", Sinn Féin president Gerry Adams said yesterday.
Mr Adams was speaking in Derry at one of the more than 100 Easter Rising commemorations held throughout Ireland yesterday.
"What annoys me the most is not the criticism from the two governments, our political opponents, or those sections of the media who are clearly delighted to have a go at us. We are used to that and we can take it.
"What annoys me the most is that a small group of individuals are not prepared to face up to their responsibilities.
"Instead these cowardly individuals will allow an avalanche of propaganda aimed at criminalising republicanism. So, let me be clear, I am not letting this issue go," he said.
"Whatever way people feel about how the McCartneys are running their campaign, this family have the right to truth and justice. And we as a party have a duty not to allow republicanism to be diminished in any way," he added.
He said that Sinn Féin in its commitment to the peace process and to achieving a united Ireland faced "more hard choices" and "more hard decisions".