TWO French magistrates appointed to investigate the murder of Sophie Toscan du Plantier are likely to commence an inquiry hearing into her killing this month.

Several Irish witnesses are expected to be called to France to give evidence.

Judge Patrick Gachon and his colleague Judge Nathalie Dutartre spent three days in Cork last month carrying out inquiries regarding French woman Toscan du Plantier's murder before returning to Paris.

They were familiarising themselves with a number of locations associated with the 39-year-old's killing as well as speaking to serving and retired gardaí involved in the investigation.

The two judges, who were accompanied by a French policeman attached to the French embassy in London, visited Toscan du Plantier's holiday home at Toormore near Schull.

They were shown where her body was found on the morning of 23 December 1996.

The visiting magistrates met several retired detectives who had worked on the original murder investigation to seek their assessment of several aspects of the case and assistance for further inquiries.

Judge Gachon and Judge Dutartre used their visit to draw up a list of civilian witnesses who made relevant statements to gardaí, many of whom will now be invited to France to testify at their inquiry into the murder.

Lawyer Alain Spilliaert, working for a group set up by Toscan du Plantier's family and friends to campaign for justice for the French filmmaker, said the magistrates' investigation was "at a critical point".

"If there is somebody they want to come and give evidence and that person does not want to come, under European law they can be compelled with a court order," he told the Sunday Tribune.

"These are two experienced criminal judges, they are very concerned by the contents of the garda file into her murder."

However, a solicitor for Ian Bailey, once the chief suspect in the killing, who has launched proceedings to sue an Garda Síochána and the state for allegedly conspiring to wrongfully convict him of the Frenchwoman's murder, said he did not believe his client could be compelled to attend the hearing in France.

"I don't accept that Mr Bailey can be compelled to leave this jurisdiction to participate in a legal process in another jurisdiction when the authorities here have fully investigated the case and confirmed that he is no longer a suspect," said solicitor Frank Buttimer.

The magistrates are working from the original garda file which was forwarded by the Department of Justice to the French authorities, and are understood to be very satisfied with the progress their inquiry has made to date.

As well as seeking to establish who killed Toscan du Plantier, the judges are also looking at obstruction of justice issues in relation to the case.

Under French law, anyone who impedes a murder investigation can be prosecuted for obstructing justice.

The French magistrates are looking closely at certain elements of the garda file specifically in relation to this issue.

Toscan Du Plantier was beaten to death at her holiday home in Schull, Co Cork, in December 1996. Nobody has ever been charged in relation to the murder.