The family of Sophie Toscan du Plantier has said the handover to a French investigating magistrate of the garda file on the murder is a significant development.
The association established by the family to campaign for the truth about the death say it remains confident her killer will be brought to justice.
Sophie Toscan du Plantier's parents, George and Marguerite Bouniol, have returned to West Cork for a Mass to mark the 12th anniversary of their daughter's murder.
In Paris Sophie Toscan du Plantier's family has established an association to maintain pressure on authorities in Ireland and France.
That pressure led to the decision by the Garda Commissioner and the Minister for Justice to hand over the garda file on Ms Toscan du Plantier's murder last month to a magistrate in Paris, Patrick Gachon, who is conducting an investigation under French law.
This afternoon the association told a news conference in Cork it believes the handover of that file is a critical breakthrough in the investigation.
Sophie Toscan du Plantier's family say they remain as determined as ever to discover the truth about her death, and they say they w ill not rest until her killer is brought to justice.