Three members of the Garda, including a superintendent and inspector, were arrested on Thursday as part of an inquiry into alleged links between members of the force and a criminal gang.
The superintendent was arrested under the provisions of section 62 of the Garda Síochána Act, 2005. It relates to Garda members disclosing information.
The inspector was questioned under the Misuse of Drugs Act, 1977-84.
The member of garda rank was being questioned about an alleged conspiracy to pervert the course of justice.
On Thursday evening, the inspector who was arrested was released without charge and a file will be prepared in his case for consideration by the Director of Public Prosecutions (DPP). He was immediately suspended from duty upon release.
The two others had their periods of detention extended, the Garda said in a statement.
The investigation is ongoing and no wrongdoing has been proven against any person under investigation.
There are concerns in the Garda that a criminal gang in the Munster area has been receiving assistance from members of the force. Specifically, gardaí believe that the gang with significant assets was tipped off about planned Garda raids.
The gang was to be raided by the Criminal Assets Bureau as its officers believed it was using a car dealership to launder drugs money.
The Garda investigation is now trying to establish whether the gang had been assisted by Garda members. The inquiry has been ongoing for some time and a number of Garda members have been suspects for a period.
The operation leading to the arrest of the three, was led by the Assistant Commissioner, Special Crime Operations (SCO), and involved personnel attached the Garda National Bureau of Criminal Investigation (GNBCI) and the Garda National Drugs & Organised Crime Bureau (GNDOCB).
A number of premises were also searched on Thursday morning as part of the operation.
Deputy Commissioner John Twomey said: "An Garda Síochána is fully committed to investigating any alleged wrong-doing or corruption involving Garda personnel, and will work with other relevant agencies in doing so.
“As this is a live and ongoing investigation, it is not appropriate to make any further comment at this time.”
Section 62 of the Garda Síochána Act states that a person “who is or was a member of the Garda Síochána or of its civilian staff or who is or was engaged under contract or other arrangement to work with or for the Garda Síochána shall not disclose, in or outside the State, any information obtained in the course of carrying out duties of that person’s office, employment, contract or other arrangement if the person knows the disclosure of that information is likely to have a harmful effect.”
Minister for Justice Charlie Flanagan said in a statement: “While I obviously can’t comment on individual cases, I expect a thorough and timely investigation.”