An SDLP motion linking the killing of Paul Quinn to current or former IRA members or their associates has been passed by assembly members.
Paul Quinn was beaten to death in October
Assembly members voted to condemn the murder of the 21-year-old south Armagh man in the Irish Republic last October.
However, Conor Murphy of Sinn Fein said he "stood by his assessment" that the IRA was not involved in the murder.
The Newry and Armagh MP accused the SDLP of "playing politics" with the Quinn case.
Mr Quinn's parents travelled to Stormont to attend the debate.
The motion was proposed by the SDLP's Dominic Bradley, who called on Sinn Fein to withdraw claims Mr Quinn was involved in criminal activity.
"I think it is shameful that Mr Murphy has not withdrawn the criminalising remarks he made about Paul Quinn after his death," said the Newry and Armagh assembly member.
"In the past members of Sinn Fein have complained about being demonised, but yet here we have a member of Sinn Fein using the same tactic against someone who is no longer with us to defend himself."
Mr Murphy said Mr Bradley's remarks were not helpful in the search for the killers.
Stephen Quinn attended a debate into his son's murder
"I would call on people to reflect on much of the politicking which has gone on around this issue in recent weeks and not let it deflect from the real task, which is finding the killers of Paul Quinn.
"Sinn Fein have not and will not seek to play politics with this issue - such public bickering does not help advance the search for justice."
DUP assembly member Jeffrey Donaldson issued a fresh call for the disbandment of the IRA Army Council.
"As I have said publicly, and my party has stated clearly, if, in the fullness in time it becomes clear and apparent the IRA were involved in this murder, that the IRA were involved in sanctioning this murder, then we will not turn our backs on the consequences of that," he said.
"That is why it is important that this issue is dealt with."
Speaking before the debate, Mr Quinn's father, Stephen, said he was hopeful the killers would be caught.
"I think the Garda and the PSNI are doing their best and I think it is going to come out who they were and all about it," he said.
Paul Quinn, from Cullyhanna, died after being attacked near Castleblayney in County Monaghan in October 2007.
Meanwhile, the Assembly Speaker has been asked to rule on whether Mr Murphy, who is regional development minister, broke the ministerial code after admitting that he had met the IRA to discuss the murder of Paul Quinn.
The DUP's Mervyn Storey questioned whether this contravened the minister's support for the police and the rule of law.
Deputy Speaker John Dallat of the SDLP said he noted Mr Storey's comments and would refer them to the Speaker Willie Hay of the DUP for a ruling.