The Dark Case of a Former Researcher Accused of Poisoning His Wife

The tragedy that happened to the elite couple

“I regret not calling an ambulance sooner. I thought she was just hungover.”

The trial of Yoshida Yoshikazu (42), a former researcher at the major pharmaceutical company Daiichi Sankyo, who is accused of killing his wife by administering toxic methanol, was held at the Tokyo District Court on October 8. During witness questioning, Yoshida spoke about the frigid state of their marital relationship and the unusual events leading up to his wife’s death.

According to the indictment, Yoshida made his wife, Yoshiko (then 40), ingest methanol, resulting in her death from poisoning in January 2022. She was found collapsed at their home, and Yoshida called the authorities. She was transported to the hospital but was later confirmed dead. Despite Yoshiko exhibiting unusual symptoms, including repeated vomiting the day before her death, Yoshida explained his reasoning for not calling an ambulance right away.

“Yoshida graduated from Hokkaido University Graduate School and joined Daiichi Sankyo, where he built a career as a researcher, including studying abroad at a university in the United States. Yoshiko also obtained her master’s degree from Kyoto University Graduate School and was an elite researcher at Daiichi Sankyo. From the outside, they appeared to be an elite couple, but they were living in a state of domestic separation, and their marital relationship had grown cold. In the courtroom, words like infidelity and visits to sex workers were mentioned” (national newspaper judicial reporter).

 

“Filthy!” she was insulted.

Defendant Yoshida appeared in court wearing a gray suit and a slim blue tie, with long bangs that fell over his eyes, leaving a striking impression. He spoke calmly in Kansai dialect about how he and his wife met as colleagues and the events leading up to the incident, including the day before.

The couple met as new hires and got married. However, soon after, rumors of Yoshiko’s infidelity within the company surfaced. Yoshida pressured her to choose between divorce or resigning from her job, and she opted to leave. Reflecting on that time, Yoshida stated,

“She was feeling down because her path to obtaining a Ph.D. and studying abroad as a researcher had been cut off.”

Later, Yoshiko gave birth to a son, but parenting stress caused their marital relationship to deteriorate once again. She began filming videos while berating Yoshida, accusing him of neglecting parenting. As their relationship worsened, Yoshida admitted,

“I wanted someone to be kind to me.”

Leading him to start visiting sex workers. When Yoshiko discovered his visits, a decisive rift formed in their marriage.

“She shouted at me to ‘throw away all your clothes because they’re filthy!’ and demanded I get tested for STDs and show her the results.”

Yoshida complied. He recounted being filmed while she yelled, “Syphilis!” and how she disinfected areas he had touched, spraying them with deodorant while calling them dirty.

What hurt Yoshida the most was being forbidden from contacting his son. Yoshiko began isolating herself and their son in a bedroom with a lock, leading to a state of domestic separation.

 

 

He won’t be made the son of a criminal.

However, even in such a situation, defendant Yoshida did not consider divorce.

“It seems that Yoshida refrained from divorce to protect his son, as Yoko’s stress started to affect him as well” (a previously mentioned journalist).

And on this day, what became clear was Yoko’s condition the night before the incident. She was repeatedly vomiting and was unable to respond to Yoshida’s calls, her speech slurred. Additionally, she had stripped naked in the hallway, entered a cold bath, and Yoshida testified that she was urinating on the floor in the bedroom. Regarding the fact that he did not call an ambulance despite noticing these abnormal behaviors,

“It may be that he was enjoying the time spent with his son and turned a blind eye. Now, I can’t really know the truth,” he stated.

Yoshida answered questions calmly, but when it came to his son, emotions welled up.

“I believe it is necessary for both parents to be together for the sake of the child. I would never do something cruel like take a mother away from her son. I am not a foolish person who would make him the son of a criminal.”

When asked about his feelings for his son,

“The one suffering the most is my son. My greatest wish is to rush to him and protect him as soon as possible,” he pleaded.

At the trial on October 11, the prosecution sought an 18-year prison sentence. Meanwhile, the defense, which asserts his innocence, pointed out that it cannot be ruled out that the wife may have consumed methanol she acquired herself and died. They argued that to ensure a murder, a large quantity of methanol would be necessary, and it is unrealistic to force a lethal dose on someone.

Is he a cold-hearted husband who poisoned his wife, or a devoted father? The verdict will be delivered on October 30.