Dieter Krombach was accused of killing his step-daughter Kalinka in 1982 at their German home. German authorities decided he had no case to answer so, in 2009, her biological father had Krombach kidnapped and brought to France.
The French father, Andre Bamberski, will eventually face a court in his turn for this vigilante action -- which became a media sensation -- but first his 76-year-old quarry will go on trial for the alleged murder.
The three-week hearing began on Tuesday in Paris' main criminal court, the three-decade-long legal and diplomatic drama having already been prolonged in spring, when Krombach was judged unfit for trial.
He entered the dock leaning on a crutch but, while his steps were careful and his voice hoarse, he appeared focused and attentive as the hearing began.
"You saw how he was talking, if you're telling me you think it's possible for him to hold on for three weeks -- there's no chance," Jan Gunter, his daughter, protested outside of court.
Bamberski's lawyer, Laurent de Caunes, shrugged off what might turn into another attempt to delay proceedings: "I didn't think he seemed very feeble. But the experts will tell us what the medical situation is."
Whatever legal manoeuvring lay ahead, Bamberski remained determined not to give up the chase at this late stage, saying: "It's certainly not revenge, it's perseverance on my part.
"If it had been revenge I wouldn't have been in the calm, confident state I'm in today," he argued before reporters.
Krombach has been convicted in absentia by a French court of "deliberate violence that led to involuntary death" -- but under French law, when someone tried in absentia is later arrested, there is a new trial.
The new trial would have been impossible, however, without Bamberski taking the law into his own hands, and employing a kidnap team to get around German legal protocol and drag the suspect to France.
His gang snatched the doctor from his home in Scheidegg on October 17th, 2009 and brought him to France, before abandoning him, trussed up, near the law courts in the border town of Mulhouse. Krombach was promptly arrested.
Bamberski has never made a secret of what he did, and expects to stand trial for his acts in several months.
French prosecutors have argued the manner of Kromach's arrest is irrelevant to the prior case against him, an argument the defence rejects.
"If you think that the way he was arrested in France has no impact on his appearance, well that to me raises a problem. Because this court is a result of that abduction," said Philippe Ohayon, Krombach's counsel.
"The aim of that abduction was this trial, so don't tell me there's no link, of course there's a link -- it's an act of vengeance and the question is who exactly was behind it all," he argued.
Kalinka, a healthy 14-year-old girl, was found dead in her bed at her German step-father's home near Lake Constance in southern Germany in July 1982. A local autopsy proved inconclusive as the cause of death.
Forensic examinations of the body did, however, call into doubt Krombach's account of the hours before the death.
His credibility was weakened in 1997 when he was convicted of drugging and raping a 16-year-old patient -- a case with no direct bearing on the French trial, but one that increased Kalinka's father's suspicions.
German judges had dismissed the case in 1987, and Germany refused to send Krombach to France in 2004 when Paris issued a European arrest warrant, on the grounds that no-one should be tried twice on the same charge.
All these arguments will now be conducted again, as the trial continues.