Gardaí have begun an investigation into an allegation that a senior investigator with GSOC attended a party with Gerard 'The Monk' Hutch.
The Garda National Bureau of Investigation is carrying out the inquiry to determine if there has been any criminality and is expected to interview the GSOC investigator who resigned last week.
The inquiry began after GSOC formally asked Garda Commissioner Drew Harris to investigate the matter.
It is the first time An Garda Síochána has been tasked to investigate the GSOC whose function is to investigate potential garda misconduct.
The Garda Representative Association said this evening that it was important that gardaí move quickly to preserve potential evidence.
GSOC has been conducting its own internal investigation after it emerged that one of its senior investigators said he had attended a party with Mr Hutch.
He took a taxi to the north inner city where a relative lives.
RTÉ News understands the GSOC investigator was renting accommodation from Mr Hutch's relative, he lived nearby and that is how he ended up at a gathering or party to celebrate Mr Hutch’s release.
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In a statement, GSOC said it has submitted a report to "the Minister for Justice outlining the action it has taken" in relation to the matter.
It said that once the organisation became aware of a potential conflict of interest involving a member of staff, it immediately removed that member's access to its systems and "commenced an initial internal investigation".
The staff member resigned shortly afterwards.
The organisation added: "It is not GSOC’s policy to investigate itself and we see independent investigation as integral to proper oversight, due process and fairness."
GSOC said it is engaging with the Department of Justice and An Garda Síochána.
The Minster for Justice Simon Harris said he "received the report he requested from the chairperson of GSOC regarding the serious matter".
A statement released by Mr Harris said he "notes that GSOC has now referred the matter to An Garda Síochána to establish if any concerns of a criminal nature arise".
"The Minister believes this is the appropriate course of action to ensure that public confidence is maintained in GSOC," added the statement.