Kenichi and Shiho Hosoya were arrested on suspicion of administering poison to kill their 4-year-old daughter Yoshiki in March 2023. (Video footage provided by a source)

Photo/Illutration Yoshiki Hosoya shortly after her birth (Provided by a source)

A Tokyo couple accused of deliberately killing their 4-year-old daughter with poison appear to have used the same tactic to murder the girl’s aunt, according to investigative sources.

Kenichi Hosoya, 43, and his wife, Shiho, 37, were arrested Feb. 14 over the death of their younger daughter, Yoshiki, in March 2023, by forcing her to ingest a toxic substance.

Tokyo police are also investigating the unexplained death of Kenichi’s sister in 2018. The Hosoyas are both executives in a hotel management company.

Kenichi has denied any wrongdoing while his wife has refused to respond to police questioning.

An autopsy of Yoshiki’s body turned up traces of olanzapine, an antipsychotic drug, and ethylene glycol, which is mainly used for industrial purposes, such as antifreeze for automobile engines.

Investigative sources said a compound from ethylene glycol was also detected in the kidney of Kenichi’s older sister after she died in April 2018 at age 41. While the sister had no pre-existing health problems, she complained of feeling unwell immediately before she died.

The sister lived in a separate unit of a condominium complex in Tokyo’s Taito Ward where the Hosoyas resided. The sister’s body was discovered several days after her death.

An autopsy was done, but nothing suspicious was found.

Even so, investigators prudently kept possession of some of her internal organs.

Because Yoshiki’s death seemed so suspicious, officers from the Metropolitan Police Department instigated a fresh analysis of the sister’s organs.

The examination found traces of calcium oxalate from the kidney. Calcium oxalate accumulates in crystal form in the kidney when ethylene glycol is ingested.

Ethylene glycol is toxic and can induce a coma or irregular heartbeat when ingested. Kidney failure arises even when a small amount is ingested, and depending on the amount consumed, the chemical is invariably fatal.

When police searched the Hosoyas’ home in August 2023 in connection with Yoshiki’s death, they seized the couple’s smartphones and computers to analyze the hard drives.

Police were able to track a purchase by the couple of ethylene glycol prior to Kenichi’s sister’s death. They also came across internet searches into the composition of the chemical and its effect on the human body.

Prior to her death, the sister visited a doctor for out-patient care and complained of dizziness. Her speech was also slurred. Because she had no pre-existing health condition, sources said police were looking into the possibility that ethylene glycol might have been responsible for her death.

Business records show that in June 2018, about a month after the sister died, Kenichi inherited the 10-floor condominium where he resided from his father. Kenichi also took over as representative director from his father of the hotel management company that same month.

Investigative sources said police were also aware of  a family squabble over who should inherit the real estate.

The August 2023 search of the Hosoyas’ residence also turned up records that the couple purchased olanzapine through overseas internet sites from about a year before Yoshiki’s death. A package of the drug was also found in their home.

Sources said Shiho told officials of a child consultation center that she took the antipsychotic drug when she experienced difficulty sleeping.

(This article was written by Yuji Masuyama, Minami Endo, Shomei Nagatsuma and Natsuno Otahara.)

Related News