A State inquiry into a secret system recording telephone calls at Garda stations will investigate the circumstances leading up to the shock resignation of the force's chief last month.
Supreme Court judge Nial Fennelly will also investigate the impact of taped conversations specifically on the investigation into the murder of French film producer Sophie Toscan du Plantier.
A legal action by former English journalist Ian Bailey for wrongful arrest in the investigation in west Cork exposed the recording system.
Manchester-born Mr Bailey was twice arrested for questioning in connection with the 1996 murder but never charged. He has always denied involvement.
After its weekly Cabinet meeting, the Government said the inquiry will examine if taped recordings expose any Garda wrongdoing in the murder investigation.
It is feared the secret recording system could threaten the outcome of past and present court cases, as well as the findings of long-running State inquiries.
Garda commissioner Martin Callinan stood down as the country's most senior police officer, claiming it was for the good of the force and his family, hours after the dramatic revelations last month.
The Commission of Inquiry - headed by Judge Fennelly - has been charged with identifying all Garda stations where the system operated since January 1 1980. It was discontinued on November 27 last year.
Under the inquiry's terms of reference, it must establish when the system was installed in each station, if there was any pre-existing system, how long it was in operation, and why it was set up.
Judge Fennelly will have to find out what authorisation was sought or obtained by the Garda for the system and its funding, and for what purposes it was used.
He will investigate the "level of knowledge" within the force of the telephone recording system and whether it was illegal.
The inquiry will report on whether others knew about it, including Justice Minster Alan Shatter, the Attorney General, the Chief State Solicitor, the Director of Public Prosecutions and the Garda Siochana Ombudsman Commission.
Further revelations of phone calls being recorded in Irish prisons may also be investigated.
Judge Fennelly has been ordered to complete his investigation by the end of the year.