A Chilean man on Tuesday denied to a French court that he had murdered his Japanese ex-girlfriend, Narumi Kurosaki, who disappeared in 2016 in a high-profile case that has spanned three continents.

"I would like to say clearly that I did not kill Narumi, I deny these accusations with all my strength," Nicolas Zepeda told the Besancon court, speaking in Spanish through an interpreter.

Kurosaki, a brilliant scholarship student then aged 21, arrived in eastern French city Besancon in summer 2016 to learn the language. She disappeared on December 4.

Her former boyfriend Zepeda, whom she had broken up with a year before, was the last person to see her alive.

"I hope sincerely that this trial will bring the truth we need to find her," Zepeda said, calling the allegation that he murdered his ex "monstrous".

The trial of Nicolas Zepeda is going ahead after he was extradited from his country to France in 2020
The trial of Nicolas Zepeda is going ahead after he was extradited from his country to France in 2020 AFP / Claudio REYES

Prosecutors allege that Zepeda was unable to deal with the couple's breakup, coming to Besancon to kill Kurosaki in her student dorm room before dumping the body in the forests of the rugged Jura region.

But so far no trace has been found of Kurosaki's remains.

After travelling from Tokyo to attend the trial, Kurosaki's mother and younger sister could be seen holding back sobs on the plaintiffs' bench.

The family's lawyer Sylvie Galley said that "they want to return home with their daughter's body" so as to hold a funeral and mourn.

Large amounts of evidence are stocked in the courtroom for the case
Large amounts of evidence are stocked in the courtroom for the case AFP / SEBASTIEN BOZON

"Narumi has been in my thoughts for the past five years and I feel her family's immense pain," said Zepeda, wearing a blue shirt and tie, from the dock under the steady gaze of her relatives.

He added that the years since her death had been a "nightmare".

Lead judge Matthieu Husson said the case "stood out by its international nature", with some witnesses set to appear by video call from Japan and Chile, and the whole trial interpreted into both Japanese and Spanish.

Clocks show the time in Tokyo and Santiago, while huge piles of documents and other evidence are heaped on a table.

The son of a wealthy Chilean family, Zepeda, now aged 31, denies any link to the disappearance of Kurosaki.

Kurosaki's mother Taeko (R) and sister Honami (C) flew in from Tokyo to attend the trial
Kurosaki's mother Taeko (R) and sister Honami (C) flew in from Tokyo to attend the trial AFP / SEBASTIEN BOZON

He met her at Japan's Tsukuba university in 2014 while working as a teaching assistant.

Zepeda's lawyer Jacqueline Laffont said her client was "almost relieved to finally be able to explain himself, to be heard" after being held in solitary confinement due to the case's high profile.

The Chilean has admitted spending the night with Kurosaki in December, claiming he ran into her by chance while travelling through France.

But several witnesses reported hearing "screams of terror" and thuds "as if someone was striking someone else" -- although none called the police at the time.

Some of Kurosaki's friends received strange messages in the following days from her social networking accounts, which police believe were sent by Zepeda.

It was more than a week later, on December 13, that a university administrator reported her missing.

The suspect had already left for Chile after spending several days with a cousin in Spain.

No sign of blood or a struggle was found in Kurosaki's student room, and all her belongings were still there apart from a suitcase and a blanket.

Zepeda turned himself in to Chilean police and said Kurosaki had been alive when he left her after spending the night together.

He quickly became the prime suspect after he was found to have gone out of his way via a forest, and to have bought matches and a container of flammable liquid.

Zepeda was extradited from his country to France in 2020.

His father Humberto, also present for the trial alongside the accused's mother, told French weekly JDD in February that the charges were "a biased accusation with no scientific proof... based on suspicions and conjecture".

But prosecutor Etienne Manteaux said last year that there was "a huge amount of technical data" relating to the case, including phone records, the locations of Zepeda's vehicle and his debit card records.

Prosecutors have also trailed "witness testimony from people close to him that disprove Mr Zepeda's version of events".