A garda has alleged that phone calls relating to the controversial Sophie Toscan du Plantier murder investigation were taped on purpose.

That is according to an internal garda document obtained by RTÉ's This Week.

In a formal statement, made by a garda based in west Cork in the late 1990s, the garda alleged that he listened back to a number of the tape recordings, which he claimed had been recorded by a colleague.

The taped calls were of phone calls to and from a key witness in the case, the garda alleged.

Ms du Plantier was found dead in west Cork in 1996.

The garda who made the statement claimed that in May 1997 he was asked by a garda colleague for his opinion on whether it was possible to tape record phone conversations to and from Bandon Garda Station.

The garda went on to allege that he later learned that the tape recording equipment had been hooked up to one particular phone in the station. 

However, he did not say where in the station the phone was located or who else may have had access to it.

He said the purpose of the phone recording was to capture calls to and from one key witness in the murder case. 

In the written statement, which was prepared in August 1997, the garda alleged that his colleague in the force who had initiated the tape recordings later allowed him to listen back to a batch of the taped conversations. 

He said the calls had been collated and stored on what he described as a C90 audio tape, according to the un-redacted document which was seen by RTÉ's This Week radio programme.

Commission of Investigation

Earlier this month, the Government set up a Commission of Investigation under Mr Justice Nial Fennelly, to examine the contents of secret tape recordings made at Bandon and other garda stations nationwide over several decades. 

Taoiseach Enda Kenny has described the contents of some of those tapes, which have not been made public, as "of grave concern."

Mr Kenny and other members of the Cabinet learned about the existence of the tapes last month, when the Garda Commissioner at the time, Martin Callinan, informed the Department of Justice about the tapes by letter.

In that letter, which has been made available on the Department of Justice website, Martin Callinan said it had emerged that calls were recorded as part of a system set up in the 1980s to monitor some calls, including 999 emergencies, coming into control rooms. 

However, he did not address the issue of whether some calls may or may not have been deliberately recorded in some cases, as alleged in this latest document.