The Garda has apologised for an oversight in which two officers travelled North to interview witnesses in connection with the murder of Denis Donaldson without the PSNI being notified.
The PSNI has accepted the apology and explanation and said that levels of co-operation between the two services remains excellent.
Mr Donaldson, a former senior Sinn Féin official turned British agent, was shot dead at a cottage in west Donegal on April 4th.
Journalists were contacted by gardaí as part of their inquiries and some resident in Northern Ireland were visited. However, the normal liaison procedures were accidentally overlooked.
Both police services issued statements last night outlining the error and insisting that working relationships were in no way affected.
The Garda said: "Part of the investigation necessitated the interviewing of a number of media people both in this jurisdiction and in Northern Ireland. Having been tasked with this job, two members of the Garda investigation team recently travelled to Northern Ireland where they met with some media people.
"The Garda officers involved had assumed that advance notice had been given to the PSNI regarding this visit through the normal liaison channels. Due to an oversight, however, this was not the case.
"The Garda Commissioner has explained the position to the Chief Constable, PSNI and apologised for this oversight."
The PSNI said in its statement: "The Garda Commissioner has explained and apologised for what happened and we accept that. Nobody should lose sight of the fact that a man was brutally murdered and the PSNI is doing its part to assist An Garda Síochána with the murder investigation. A detective superintendent from the PSNI's serious crime squad has been appointed as a liaison officer. This officer has been in regular contact with An Garda Síochána and they have had face-to-face meetings." It was stressed that those interviewed were not suspected of any crime.