Ian Bailey, a 62-year-old former freelance journalist, has always denied killing Sophie Toscan du Plantier, the wife of a prominent French film producer, at her holiday home in County Cork in southwest Ireland.
But Bailey refused to appear at the French trial that opened Monday, and Dublin has rejected two previous requests to extradite him, citing insufficient evidence.
In its ruling, the court said there was "sufficient evidence" to justify the conviction despite Bailey's "constant denials".
Toscan du Plantier's 38-year-old son, Pierre-Louis Baudey-Vignaud, fell back into his seat upon hearing the verdict, while her 92-year-old father, Georges Bouniol, wiped his eyes with a white handkerchief.
"After 22 years of waiting, 22 years of suffering, 22 years of questions, the judges have convicted Ian Bailey who killed my mother," Baudey-Vignaud told reporters afterwards.
"It's a victory for the family, for the truth," he added. He was 15 years old when his mother was murdered.
Injuries to her hands showed that Toscan du Plantier had fought to defend herself, and a large rock and a bloodstained concrete block were found near her body.
Bailey, who lived near her house, was found with scratches afterwards which he attributed to a Christmas tree and cutting up a turkey for dinner.
A lawyer for Bailey in Ireland described the verdict as a "miscarriage of justice", criticising the French for having shown "total disrespect to the Irish justice system".
"He is innocent of the crime… Our public prosecutor has long since decided that this is the case," Frank Buttimer told AFP.
He added that he hoped the Irish courts would be "consistent with their previous decisions" not to extradite Bailey, who now sells pizzas in the village of Schull where the murder took place.
The Irish government has refused to send him to stand trial, saying he was twice arrested for questioning by police who failed to find any substantive evidence.
It has also cited the lack of an extradition agreement with France, which moved ahead with a trial following a complaint by the family of the victim in 1997.
French prosecutors had sought a 30-year prison term, accusing Bailey of a "barbaric crime committed against a woman… who no doubt endured three minutes of terror."
During the trial, the three judges hearing the case were told that Bailey had given details of the crime in his own reporting that had not been disclosed to the press.
A lawyer for the victim's family, Marie Dose,Read More – Source