YOKOHAMA -- Kanagawa Prefectural Police are poised to build a criminal case against a former nurse on suspicion of fatally poisoning a second victim at a local hospital, investigative sources said.
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Prefectural police intend to serve a fresh arrest warrant accusing Ayumi Kuboki, 31, who is under arrest on suspicion of fatally poisoning inpatient Sozo Nishikawa, 88, at the then Oguchi Hospital in Yokohama in September 2016, of murdering another inpatient, Nobuo Yamaki, also 88.
During questioning, Kuboki admitted that she administered disinfectant to other patients. Prefectural police investigators are trying to clarify the circumstances surrounding the case.
Prefectural police began questioning Kuboki, who had been looking after inpatients on a fourth-floor ward for end-of-life care at the hospital, currently named Yokohama Hajime Hospital, on June 29. Both Nishikawa and Yamaki were sharing the same room in the ward. The following day, Kuboki acknowledged that she administered disinfectant to patients, sources close to the investigation said.
Investigators became convinced that Kuboki was involved in the incident after an eyewitness reported having spotted Kuboki entering Nishikawa's room shortly before his condition worsened, and traces of a disinfectant was detected on her uniform.
However, Kuboki's acknowledgement that she administered disinfectant to patients was a decisive factor that led to her arrest.
As to the motives behind her alleged crime, Kuboki was quoted as telling investigators, "My work at the time of the death of each patient was troublesome," "I wanted to time the deaths of the patients I was looking after to my convenience," and "I hated to be suddenly summoned."
According to the sources, Kuboki allegedly used a syringe to inject disinfectant into the side tube of Nishikawa's intravenous drip tube, and injected such an agent into an intravenous drip bag for Yamaki.
Police suspect that she attempted to prevent patients she was looking after from dying during her own work shifts.
Kuboki, who joined Oguchi Hospital in the spring of 2015 after graduating from a nursing school, was quoted by the sources as saying that she administered disinfectant to about 20 people from about two to three months before the incident came to the surface.
However, it is difficult for police to investigate these cases because the patients probably include those who died from their original illnesses, or those who died before the hospital noticed the deaths of inpatients under mysterious circumstances.
Autopsies have shown that Nishikawa and Yamaki died of poisoning from a surface-activating agent contained in the disinfectant.
At almost the same time, a woman in her 70s and a man in his 80s died at the same ward. However, only blood samples are preserved for the woman, while the man died from a cause other than poisoning from a surface-activating agent.
Prefectural police are apparently aiming to build up criminal cases against Kuboki over the deaths of the woman and the man.
However, one of the investigative sources pointed out that it is difficult to form cases over the deaths of these two other people. "Even if the suspect were to admit to her involvement in these cases, it'd be no easy task (to build up criminal cases against her)," said the source.
(Japanese original by Yuhi Sugiyama and Tsumuki Nakamura, Yokohama Bureau)