The failure to bring Sophie Toscan du Plantier's killer to justice “must forever remain a deep shame”, Tanaiste Micheál Martin said.
The body of Mrs Toscan du Plantier was found brutally beaten outside her holiday home in Schull, West Cork, in December 1996.
The prime suspect in her murder was Ian Bailey, who died in January aged 66. He was convicted in absentia by a French court in 2019 but has always denied any involvement.
“Her murder 28 years ago was a profound shock to us and remains so to this day,” Mr Martin said.
“The brutal attack that took her life is forever etched in our consciousness, and the failure to achieve justice and bring her killer to justice is and will always be our deepest shame.
“The terrible suffering of her family and everyone who knew her was made much worse by the fact that our system failed to live up to its obligations to Sophie.”
Mr Martin said there was “no doubt” the case was thought-provoking.
“There is still reason to doubt that the principles and procedures under which we deal with these cases always serve justice,” he said.
“The simple fact is that we failed to do our duty to find and convict a bloody killer, and our system blocked alternative paths when others were unwilling to accept our failures.”
The Tánaiste said that in his own assessment the body of evidence against Mr Bailey was “enormous”.
He described Bailey as “a violent man who beat his partner so badly she had to go to hospital” and his psychological profile was “an impulsive narcissist and misogynist”.
“When you look at the details of this case and the scale of the evidence, it is very, very difficult to understand why this evidence was not presented to the jury,” Mr Martin said.
He said that while the Irish justice system had its strengths, including the fact that it was independent and judges could not be subject to outside pressure, it could be acknowledged that it had failed in Ms Toscan du Plantier's case.
Mr Martin paid tribute to Ms Tuscon du Plantier and her family, telling of their three-decade wait for justice.
Following Mr Martin's speech, Ms Toscan du Plantier's uncle, Jean-Pierre Gazo, called for an investigation into her death and urged Mr Martin to support the cause.