A former nurse has admitted tampering with intravenous drips in a mass poisoning case that police believe led to the deaths of dozens of patients at a hospital in Japan two years ago.



Ayumi Kuboki, 31, was arrested at the weekend on suspicion of killing Sozo Nishikawa, 88, by injecting his intravenous drip bag with disinfectant when she was working at Oguchi hospital in Yokohama.

She has since told investigators that she also poisoned another 88-year-old man, Nobuo Yamaki, who was being treated in the same fourth-floor room as Nishikawa, and may have killed another 20 patients using the same method, according to the Asahi Shimbun newspaper.

After her arrest on Saturday she reportedly told investigators that she dreaded having to deal with grieving relatives and so timed her actions so the patients died when she was not at work.

About 48 patients at the hospital died in unusual circumstances over a three-month period in 2016, including five in a single day.

Police launched a murder investigation after traces of benzalkonium chloride – a chemical present in the same disinfectant used to clean the nurses’ station – were found in Yamaki and Nishikawa.

Staff found puncture marks in 10 of about 50 unused drip bags stored near the nurses’ station on the same floor.

Kuboki initially denied any involvement in the deaths, telling media that she was shocked and felt sorry for the victims and their families. She added that she had not noticed anything unusual during her shifts at the hospital.

Japanese media quoted her as telling police after her arrest that she had administered the disinfectant to “about 20” other patients, adding that she only targeted those who were gravely ill. The victims include those whose conditions were not serious, however.

Police conceded in 2016 that they were unlikely to establish the cause of every suspicious death since many of the bodies had been cremated.

Former colleagues said they were shocked to learn that Kuboki, who started working at the hospital in 2015, had been arrested. “We had had no inkling that she was a problem employee,” a member of staff told the Asahi.



An employee who had worked with Kuboki at a different hospital said: “She was the kind of person who was hard to figure out … but she was considered competent.”

Kuboki, who left Oguchi hospital last month, first aroused suspicion after her uniform was the only one among those examined by police that carried traces of benzalkonium chloride.