Mrs Toscan du Plantier was 39 when she was found beaten to death in Schull, west Cork, on December 23, 1996. A bloodied rock and a concrete block were found nearby, while injuries to her hands indicated the socialite had tried to defend herself from her attacker.
When her only child Pierre-Louis Baudey Vignaud, now 38, visited the bohemian area of Cork last week urging witnesses to testify, he said: "My mother, Sophie, is not a ghost, she is the victim of human cruelty and violence which has no place here.
"Sophie fought like a lioness against the most atrocious violence there is. I can't bear the thought of her blood seeping into your soil."
In turn, lawyers for Bailey – who still lives nearby – were outraged that the victim's son had been allowed to make what they regard as defamatory statements about their client.
Even more so that the victim's son made his plea from the pulpit at a local church, the Church of Our Lady, Star of the Sea and St Patrick in Goleen, West Cork.
Dominique Tricaud, Bailey's French lawyer, said: "Ireland's attorney general has examined everything and wrote a 96-page report that concluded with dismissal of the case."
In France, individuals who attack the country's citizens abroad can be prosecuted despite alleged offences taking place outside French jurisdiction.
As the case opened yesterday afternoon, there was a dramatic silence in court when Frederique Aline, president of a three-lawyer panel hearing the case, asked: "Is Mr Ian Bailey present or represented?"
The judge then made clear that neither Bailey nor his counsel had submitted a letter to the Paris Assizes explaining why they had stayed away.
The court heard Bailey had repeatedly changed his alibi in the days and weeks after the discovery of Mrs Toscan du Plantier's body.
"He first of all said he was in the pub with his partner," said Judge Aline. "Then he told how he had spent the night at a friend's. Then he said he slept at home but went out to work in his studio, which was about 50 meters [164ft] away."
At least 22 witnesses who were named on a summons list were also absent at court yesterday.
These included a former British soldier called Martin Graham, who was said to have been given cash and cannabis by Irish detectives to draw a confession out of Bailey. When it was announced he would not be turning up in court yesterday, a barrister told the court: "There's a good reason for that – he's dead."
Bailey's long-term partner Jules Thomas and her daughters Saffron, Ginny and Fennella also were summonsed but stayed away.
Mrs Toscan du Plantier was married to the Gaumont cinema producer Daniel Toscan du Plantier, who worked with directors including Federico Fellini and Ingmar Bergman, and who died in 2003.
Bailey, who was born in Manchester, has said he fears he will be the victim of a "farcical show trial". He was arrested twice in Ireland but released without charge.
"I know that I had nothing to do with this and I am going to finish up as a convicted murderer," he said last week.
French authorities have indicated that if they can achieve a conviction they will immediately push to have Bailey brought to France, acting on an existing European Arrest Warrant.
The trial continues.
