Today marks the 26th anniversary of the killing of the 39-year-old French filmmaker at her holiday cottage in west Cork in 1996.
A twin-track investigation into the murder by gardaí and a cold-case review team has been under way for six months, but an enormous amount of work remains to be done.
Nearly 10,000 separate pieces of information compiled over 26 years have to be reviewed, and the process has been complicated by the deaths of 10 witnesses and garda members.
Gardaí said the cold-case review, under Det Supt Des McTiernan, will not interfere with the continuing investigation by a West Cork garda team under the direction of Supt Joseph Moore.
In contrast, it aims to complement that investigation by reviewing all possible evidence, considering new forensic testing techniques and re-examining all witness statements.
The cold-case team hopes to be able to make recommendations on the basis of their review, with the aim of ensuring the updated garda case file secures a decision to prosecute by the DPP.
Ian Bailey (65) was convicted of the killing by a French court in May 2019, but has always protested his innocence. He says he “stands ready and waiting” to co-operate with gardaí in any way he can.
He said he believes the cold-case review will exonerate him of any involvement in the murder and finally clear his name.
Bailey was arrested twice by gardaí in relation to the case in 1997 and 1998, but was released without charge on both occasions.
He has described the Paris prosecution as “a mockery of justice” and “a show trial”.
On three occasions the Irish courts have refused French requests for the Manchester-born law graduate to be extradited.
Meanwhile, Ms Toscan du Plantier’s family will remember her today at a private ceremony in Paris.
Each December, the relatives – led by her son, Pierre-Louis Baudey-Vignaud – hold a private memorial to mark the anniversary.
Mr Baudey-Vignaud’s eldest daughter is named Sophie in honour of her grandmother.