A key witness in the Sophie Toscan du Plantier murder investigation said she received "constant" calls from a garda pleading with her to wrongly implicate Ian Bailey in the French woman's killing, according to documents seen by RTÉ's This Week.

Former shopkeeper Marie Farrell gave a lengthy statement to gardaí in 2006, in which she claimed that a garda gave her a special garda-issue mobile phone for the exclusive purpose of discussing the case away from the attention of other gardaí.

She also claims that this garda instructed her to make calls from two public phones in the village of Schull to avoid arousing suspicion over phone traffic between gardaí and her home or work numbers, according to the document.

Ms Farrell said that from early 1997 onwards she was receiving "endless" calls from certain gardaí, who were asking her to make statements containing "fictitious events involving Ian Bailey", according to a copy of the statement, which has been seen by This Week.

She also claimed that a garda rang her in May 1997 to express concern over a possible tabloid news story relating to another witness named Martin Graham, who claims to have been offered cash and drugs to obtain information against Mr Bailey.

She said the garda told her that they were "in the shit" and he pleaded with her to leave his name out of it if she was quizzed on the matter.

However, she said he rang her back sometime later that year and claimed that gardaí in Dublin had managed to stop the story being published.

He also claimed that gardaí had put pressure on Mr Graham who had since travelled to England. The garda was confident he would not be coming back, she said.

More than three dozen phone calls between Ms Farrell and gardaí have been recently uncovered, along with scores of others between gardaí, journalists and other witnesses, as well as among members of the force.

The Taoiseach said last week that the content of some recordings relating to the murder case were a "cause for concern".

Enda Kenny said that the terms of reference for a Commission of Investigation into tape recordings made at certain garda stations will be finalised on Tuesday.

It is known that some of those calls relate to conversations between gardaí and Ms Farrell during the investigation into Ms Du Plantier's murder at Toormore, near Schull in west Cork, in December 1996.

The Garda Press Office said it would not be appropriate at this time to comment on any of the issues.