The son of Sophie Toscan du Plantier says he has been living a nightmare for every day of the last 25 years.
Pierre-Louis Baudey-Vignaud was speaking as Gardaí are to conduct a full review of her case.
The French filmmaker was beaten to death with a brick and a rock outside her holiday home in Schull in west Cork, two days before Christmas in 1996.
Pierre-Louis told Moncrieff this review was a long time coming.
"I think this new team is quite busy, and so they need to study the case.
"And they were waiting for the DPP decision.
"I've been waiting for 25 years for the justice - so for me, it's not a so long delay".
But he says the entire process has been a nightmare.
"Twenty-five years looking for justice, taking me a lot of time to fight, to respect and to take some time for speaking with you, for speaking with the Irish police, to the French police, to do the trial.
"I have to pay a lot of lawyers - so it's a nightmare, it's still a nightmare.
"You can never find some peace with this sort of thing.
"Every day, every week for 25 years I have information, I have an exchange with journalists, with people in Ireland, with people in France.
"So every day it's a nightmare".
He says he believes pressure from different areas led to this review.
"I think there is a lot of pressure from the public opinion, from the media, from the European Commission - because Ireland decided to not extradite [Ian] Bailey to France.
"I think also there is a lot of pressure from the people in Ireland.
"In a way, the Irish justice need answers for the country and for the people.
"[With] this new investigation, the DPP recognises that the Gardaí and the team of the DPP made some mistakes during the previous investigations.
"So they need to go further - and maybe with the new technologies, they think that they can prove something".
'People in Ireland are more angry'
Pierre-Louis believes Irish people are more angry than he is.
"There is still a murderer in Ireland, so if I was Irish and I was living in Ireland I should be angry.
"I think most people in Ireland are more angry than me.
"I keep fighting for the justice of my mother and the justice of the Irish people".
While Ian Bailey, who was convicted in absentia in Paris in 2019 and sentenced to 25 years, says he will cooperate in any way that he can.
"My prayer for a quarter of a century has been that the truth at some point would come out before I was dead.
"I hope there will be [a successful outcome] and if I can give any assistance, I will be doing that," he told Newstalk.
"I would hope there would there be an acknowledgement - if not the discovery of who was the murderer of Madame Sophie Toscan du Plantier - an acknowledgement that it wasn't me.
"That's my hope... and any assistance I can give to An Garda Síochána, I will be giving", he added.